It’s a short form of the twitter hashtag #FollowFriday. Follow Friday is a simple method of recommending people to your followers on twitter.
Hashtags on twitter are a way to tag tweets with a topic that can be used for searching purposes. Adding # to the beginning of any word turns it into a hashtag. Clicking on a hashtag returns a search result page of tweets containing the hashtag.
Anytime on any or every Friday, start a tweet with #FF or #FollowFriday and mention (add the @ character to their twitter user name) the people you want to recommend.
Follow Friday Helper makes creating Follow Friday posts easier by filtering the list of people you follow and allowing you to just click on the names instead of typing them in.
- What is #ff and how to use it properly (successnetwork.wordpress.com)
- What is #FollowFriday and how to do it correctly? (allisterfrost.com)