"There are a couple of unbelievably enthusiastic girls in the US who seem to want to know 'what's up?' with all 18 members of the St John's College Choir every Monday morning at 11am," says Dom.

He's a friend from university whose simultaneous membership of three august British institutions (Cambridge, St John's and their famous choir) has delivered him a great many friends on Facebook whom he wouldn't recognise if they turned up at his door carolling in bunny ears.

Having graduated, he has begun the methodical work of deleting pointless online connections one by one. By so doing, he is joining one of the most satisfying and cathartic movements around: the unfriend trend.

The insider's term for getting rid of Facebook friends is "culling", and it has inspired a cottage industry of websites and blogs delighting in its cruelties and amusements, including one that informs people of their fate and records their reaction.

I started culling in earnest this summer, and I haven't stopped since. Last year I think I had about 800 friends and after a few deletes over the weekend I'm now down to 497 - not a bloodbath of biblical proportions but a pretty solid start. One friend made the mistake of culling after a few drinks and went too far, ending up with only 50 friends and having to re-add many of them in the following days.

Like all the big divisive movements in history, culling comes down to semantics. The Oxford Dictionary says a friend is "a person with whom one has a bond of mutual affection", although it's one of those words whose meaning is greatly clarified by the prefix "real". Furthermore, a study earlier this week revealed that the average person only has two close friends or confidants, down from the three suggested by a similar study 25 years ago.

No one truly thinks Facebook friends are all real friends but what are they? The criteria I have broadly applied for keeping people in my social network is: are they people with whom I would enjoy a one-on-one drink? That doesn't necessarily mean that I know them very well but the "social pint formula" (as I hope it will come to be known) provides a workable model for culling.

The 300 or so people who no longer have access to my amusingly entitled photo albums and occasional status updates are an eclectic bunch. Some are friends of ex-girlfriends whom I never knew and who - for various reasons - I'm grateful have not tracked me down and killed me. Others are gap-year acquaintances, classmates who I added in that first spate of Facebook zealousness or the recipients (or - more rarely - initiators) of drunken "adds" after nights out.

I'm not doing it because I'm worried about privacy, or because I dislike many of the cullees. I just don't want to be in a network of people that isn't meaningful. The old rationale was that you're connected with anyone you had spoken to but more and more friends seem to be realising that the only photos and statuses they really want to spend time looking at are the ones of and by people they know, at least a little bit.

It is what AOL's "digital prophet" David Shing meant last month when he predicted that the next phase of online usage will be about unfriending and unfollowing, as people try to reduce the "noise" on their social networks and make them more relevant again. Shing said the age of treating the web as a popularity contest was over.

Culling has its downsides. Jason Graham, a City worker who culled one friend a day last year and wrote about why each one deserved the chop on his blog, says "there were a few people who were quite angry about it". And another blog where the writer posted on each victim's wall why they were being deleted ("I culled you because I don't know you") and took a screen grab of their response is very short. Perhaps because the author was hunted down in a terrible but well deserved revenge killing.

The social networking sites have pre-empted the desire of users to rationalise their networks by making unfriending more time-consuming and creating mechanisms ("lists" in the case of Facebook, or "circles" for Google+ ) that allow us to specify close friends, acquaintances or colleagues. One (real) friend told me she would rather limit what certain people can see than unfriend altogether, which might offend a useful future contact.

The unfriend trend is happening because the novelty of arbitrary networking is over. Instead we want to remember what our social relations really mean. "Culling is valuable because it keeps things in perspective," says Dom. "I don't have 740 friends. In fact, I've probably got about seven and another 100 or so people that I'm delighted to see when I do. Why tell myself otherwise?"