Some journalists are fond of defining it with the sort of one-liner that says something like, "news is what you didn't know yesterday". Such definitions may be quite useful as media studies exam questions, but they're not much help when you're making hour-to-hour decisions about what to put in a newspaper. The truth is that editors put things in their paper because their guts, like a cook's nose, tell them it's what their readers want.
Which is why that letter was interesting - because it specifically defined news as what's going on in "Burundi, etc ... not pictures of butterflies".
Intriguingly, almost the next letter I read came from a reader objecting to our carrying a front-page story and picture about the recent massacre in Burundi, on the grounds that it was distressing. And the next letter after that came from someone who was "delighted by the butterflies, not least because they made a break from all the scenes of carnage". Which just goes to prove you can't please all the people, all the time.
You can try though - and last Saturday's butterflies did seem to please an awful lot of readers. The only item in the postbag outnumbering congratulations for our lepidopteral photomontage was letters about abortion. The most intriguing aspect of this story, to me, has been the way in which the moral focus has shifted. It started on the woman and her twins; it shifted to the pro-lifers; then to the medical ethics; then to the journalistic ethics of searching out the woman; and now it has shifted back to the doctor and the ethics of disclosure. It makes you wonder whether anyone can remain clear-eyed about moral absolutes - let alone news values.
Is it not also striking that we regard the manner of political campaigning (this week's demonisation of Tony Blair by the Tories, for example) as being as significant a political event as any argument over policy? I was taught that style is inseparable from content: if that still holds true, surely the style of an election campaign tells us something about the ideas in its perpetrators' heads?
And if news is defined as what's new - well, A-level results wouldn't figure much. As a former education correspondent, I can confidently say that I have seen all of this week's A-level stories several times before. In the education world, there is nothing new under the sun. But that doesn't diminish each year's drama: the moment, which most students will never forget, of opening that envelope and feeling either shattered, or relieved, or elated beyond expectation. The results are news every year because they touch so many people - parents, brothers, sisters, friends. But they are also good news, because so many young people now go on from their A-levels to university, giving us a vastly better educated workforce.Anyone who really thinks we are going backwards educationally has forgotten how bad it was when we kept college education for the very few.
Still, those who missed a proper education the first time round can catch up with our DIY University summer school, appearing each weekday on the Commentators page. Next week you get DNA, economics, and a bundle of other wonders. Stick with it.