Originally, I thought that the Facebook like button displays the number of people who had clicked on it. However, I have experienced some behaviour that made that obviously impossible (such as the number shown by the button being greater than the actual number of people who had seen the post).
I did a little research on the Internet on the subject and I’ve found a little shocking truth—the number is actually the number of interactions with the webpage on Facebook, where an interaction is defined as any permanent action that any user takes in any place that links to the webpage. For example, when someone
- includes a link to the webpage in a status update
- likes such a status update
- posts a comment on such a status update
it always counts as +1 in the like button counter, even if all the actions are taken by the same person. For example, if I post a link to my post and two people start arguing over it in the comments, posting 20 comments overall, the counter will immediately show 21 as the number of likes, even though perhaps only three people have actually seen the post.
So the conclusion is: If you see a high number of Facebook likes on a website, but only a few tweets and Google +1s, it doesn’t mean that Facebook is much more popular as a social network, or that the post itself is more popular among Facebook users. It is just that Facebook counts everything as a like, even if people do not intend it to.