#FF is short for #FollowFriday. It’s a Twitter trend created way back in 2009 and has become a customary Friday activity ever since.
An #FF is a shout out, a show of appreciation, a nice recommendation. Each Friday you suggest Twitter profiles to all of your followers that you appreciate and enjoy. The idea being that your #FF suggestion will encourage others to check out that profile, generating more followers for them. It’s a really nice thing to do within the Twitterverse.
The hashtag (#) is added to create a clickable link and group all the #FF messages on Twitter together making them easily searchable.
Here is an example:
Do you partake in #FF? Make sure to follow us! @PRowlPR