Hashtags are often abbreviated or a little wacky (brevity and humor being two pillars of social media). The insider speak can leave newcomers confused. Here's a key to some hashtags that have made the rounds:
#tbt: Adorable childhood photos en masse? Must be #throwbackthursday.
#ff: It's a bit old-school now, but help your friends' audiences grow on "follow friday."
#winning: A remnant of Charlie Sheen's very public meltdown. Sincere or sarcastic uses apply.
#nodisrespecttobenaffleck: One of the many gifts of Kanye West's Twitter account. Use as you see fit.
#ootd: Fashionista selfies show off the "outfit of the day."