look up any word, like fap:
 
1.
The hour, usually between 8:30 and 9:30PM, when more of your friends are signed onto Facebook than usual.
Person 1: Hey. It's Facebook hour and 49 of my friends are signed onto Facebook!
by gamerdude949 May 26, 2009
 
2.
While a regular hour has sixty minutes, a Facebook-hour is usually shorter; due to the unnecessary amount of time spent on Facebook when one should be doing other activities.

It can vary from fifty minutes, all the way down to just fifteen minutes left on an hour.
Mark: Why did it take you five hours to do your math homework yesterday?

Tim: It took two and a half, actually, but was on Facebook half the time

Mark: Oh, so five Facebook hours?

Tim: Yes
by Norway90 March 06, 2011