A – Album: Or, more accurately, the concept album. It may seem alien to the iPod generation, but for prog rockers, the ritual of the long player – single, double or even triple disc – was sacrosanct. And no self-respecting LP in the mid-70s came without a decent saga attached. Genesis's The Lamb Lies Down on Broadway tells the story of a Puerto Rican delinquent named Rael, who embarks on a nightmarish subterranean adventure in search of his brother. Yes's preposterously entitled Tales from Topographic Oceans was written around a footnote in Paramahansa Yogananda's Autobiography of a Yogi, while Tarkus, by Emerson, Lake & Palmer (ELP for short) tells of a battle between a mythical manticore and an armadillo – not a theme yet pursued by JLS.
B – Blokes: Maybe some women did like prog, but it was basically music by men for men, normally with beards. Female personnel were few and far between in the leading acts of the day and non-male fans tended to shun the allures of King Crimson's Larks' Tongues in Aspic (Parts I and II) in favour of glam-tinged quasi-proggers such as David Bowie and Roxy Music.
C – Canterbury: Cathedral city in the garden of England, best known for its cream teas and cricket ground was, for a short period in the late 60s and early 70s, the unlikely crucible of British psychedelic talent that was to pave the way for the progressive rock scene a few years later. Famous sons include Soft Machine, Caravan and Spiro Gyra.
D – Dungeons and Dragons: No one could really sit through those long albums and their never-ending guitar solos without some distraction. First released in 1974, the fantasy role-play game – known to aficionados as D&D – provided the perfect bedsit amusement.
E – Excess: Whereas conventional rock'n'roll prided itself on its visceral simplicity, proggers took the basic chord structure and added their own fancy-pants sixths, sevenths and eighths and further confused matters with a series of baffling time signatures. Ever more pretentious and magniloquent, tracks swelled with sprawling, pseudo-classical movements and overtures.
F – Flares: Progressive rock was about music, not fashion, but a pair of testicle-crushingly-tight flared trousers was de rigueur for the Genesis generation. Typically worn with a slightly too-small shirt, a denim jacket (complete with badges and patches) or an Italian combat jacket with Marillion's harlequin on the back, the look was artfully set off with a pair of platform shoes and a rolled-up cigarette.
G – Gatefold cover: One of the saddest consequences of the demise of the vinyl record has been the loss of the album cover as art (not to mention it as being an invaluable platform for rolling spliffs). The gatefold sleeve had been popularised by The Beatles among others, but in the spirit of excess it became a near compulsory feature of prog albums providing a conduit for lyrics, band photographs and other general musings. Artists including Roger Dean – who worked with Yes – produced extraordinary fantasy-inspired images that set the scene for the musical odyssey that awaited the listener within.
H – Hawkwind: With 26 studio albums – the most recent, Blood of the Earth, released only last month – and 11 live albums to their name, Dave Brock's Hawkind have been the doughty perennials of the British rock scene, straddling genres from progressive to psychedelic. Among their more colourful collaborations was teaming up with the sci-fi author Michael Moorcock.
I – Instrumentals: Prog didn't invent the instrumental, but it certainly produced the best selling example of the (largely) vocal-free album. Mike Oldfield had been rejected by all the major labels before he presented Richard Branson's nascent Virgin with a cassette recording of his two-movement magnum opus Tubular Bells in 1973. The musician played all 20 instruments himself (including the tubular bells) and his record went on to sell nearly three million copies in the UK and become a dinner party – as well as a chill-out – classic.
J – Jerusalem: Proggers had a natural affinity for Blake's elegiac poetry and Carl Palmer's adaptation of Hubert Parry's rousing hymn, taken from ELP's fourth album Brain Salad Surgery (said by fans to be a euphemism for oral sex) scandalised classical music buffs, who resented the long-haired trio's venturing into the "serious" sphere. The BBC accused the band of degrading the original and banned the track from being played on air.
K – Krautrock: We might like to think of prog as a very British phenomenon, but in Germany a similar movement was gathering pace, too. Among the most celebrated exports to be championed by John Peel (who famously dismissed ELP's overblown 1970 Isle of Wight performance as a "waste of electricity") was Tangerine Dream. The Berliners liked to test their fans' endurance to the limit by playing extremely loudly (134 decibels) and sometimes for several hours at a time often in complete darkness.
L – Line-up changes: No self-respecting prog band would stick with the same members – it was a badge of honour for musicians to switch allegiances and depart on solo projects. Both Rick Wakeman and Peter Gabriel took leave from the mother ship selling millions of albums, while bands such as Atomic Rooster evolved from The Crazy World of Arthur Brown and went through 12 members in their two incarnations.
M – Minimoog: Workhorse analogue synthesiser invented by Dr Robert Moog, who earned his PhD in engineering from Cornell University. It was elevated to front-line instrument alongside the guitar by prog rockers such as Yes and Tangerine Dream.
N – Nineteen seventy four: The year of President Nixon's Watergate resignation, the start of Ceefax and the return of the first Skylab crew to Earth was also the high-water mark for prog rock. There were two albums from Yes and King Crimson, Hatfield and the North's debut and works from Rick Wakeman, Supertramp and Genesis. A vintage year.
O – Orchestra: Many prog bands simply refused to believe they were not orchestras. The Electric Light Orchestra even called itself one. Fancy fretwork on the guitar and keyboard players who could read music – such as Royal College of Music-educated Rick Wakeman – put most of the bands one up on their rock'n' roll counterparts. ELP famously recorded versions of Mussorgsky's Pictures at an Exhibition and Aaron Copland's Fanfare for the Common Man.
P – Punk: If video killed the radio star at the beginning of the 1980s, it was the turn of Johnny Rotten and the drainpipe trouser brigade that took the wind out of the prog rockers' voluminous flares. Some now doubt that prog ever really went away. Frankie Goes to Hollywood's 1984 triple-platinum selling Welcome to the Pleasuredome was a double concept album in a gatefold sleeve with an 18-minute title track based on a poem by Coleridge. How prog is that?
Q – Magazine: In 2005 the influential music magazine published its top 40 of the best prog rock albums ever. Number one was Pink Floyd's Dark Side of the Moon while Radiohead's OK Computer controversially ranked at 10 though the band hated to be described as prog.
R – Rotters Club: Author Jonathan Coe took the title of his best-selling book from Hatfield and the North's second album. A group of Birmingham school boys battle to comprehend the heartbreak of adolescent love alongside the semiotics of a Robert Fripp guitar solo.
S – The Stranglers: They may have styled themselves punk bully boys who cared little whether they offended the politically correct attitudes of the day with the occasional misogynistic lyric and on-stage stripper, but for the origins of the band's synthy-bassy sound one needs only listen to Rick Wakeman's 1975 Merlin the Magician. Proggers by any other name.
T – Theatricality: Despite – or perhaps because of – the occasionally torpid propensities of the music, many prog outfits relied heavily on stunning visual displays and atmospheric settings such as ancient amphitheatres or historic ruins to spice up their work.
U – Utopia: Just to prove that the Americans were able to get in on the act too, Todd Rundgren enjoys a place of honour in the pantheon of proggers. His self-titled debut album contained only four tracks and ran for almost sixty minutes in total. Side two contained just a single 30-minute track – The Ikon.
V – Van Der Graaf Generator: Endorsed by no less a figure than hippy-hating punk emperor Johnny Rotten – who considered himself a proper fan – the dark melancholy of Manchester's finest proggers has endured the contempt of punks and continues to influence. Still gigging and recording a new album.
W – Wondrous Stories: Taking its name from the Yes track of the same name, this compilation album charting the rise of prog was a surprise hit this year.
X – Brand X: Prog supergroup/ jazz-fusion session band that included Phil Collins on drums.
Y – Yodelling: Dutch flautist Thijs van Leer and guitarist Jan Akkerman's classical-inspired band Focus scored two hits in the early 1970s with Hocus Pocus and Sylvia. The former introduced the pop world to the delights of yodelling and falsetto singing and was used by sports firm Nike in its 2010 World Cup advertisements.
Z – Zappa: Musician, composer, conductor, commentator, libertarian, director, Frank Zappa once described rock journalism as "people who can't write, interviewing people who can't talk, for people who can't read" and though he may have well have shown disdain for the label, his album Hot Rats is considered one of the genre's masterpieces.