What does #oomf mean on twitter?
The "#" symbol is referred to as a hash tag on Twitter, and it's used as a way for Twitter users to categorize their tweets, a form of keyword for searching.
So in this case everyone that uses the #oomf "hash tag" is talking about someone that follows them on Twitter or a friend that they prefer not to name directly.
The birth of the hashtag came on August 23, 2007 when a Twitter user named Chris Messina tweeted the following: “how do you feel about using # (pound) for groups. As in #barcamp [msg]?”