What’s in a Twitter fave? It’s a gesture – just the click of a button – that can mean any number of things given the context.

We’ve developed an entire ecosystem of Twitter faves over the past few years. There’s the hate-fave. The flirt-fave. The fist-bump fave. 

Now, researchers have gone one step further and developed what purports to be a scientific taxonomy of favoriting behavior, based on survey responses from 606 active Twitter users. The biggest surprise? Over a third of Twitter users said they weren’t even aware the favoriting function existed. Among the rest, only 3/4ths of users had ever favorited a tweet. 

The researchers asked the remaining 290 users open-ended questions about why they favorited things. They coded the responses into a number of categories, and the taxonomy above was born.

The most popular reason for faving something? People simply liked the tweet. For many people it’s analogous to Facebook’s “like” button. Not surprisingly, bookmarking things for later reading or recall was the second most popular reason. 

Others used it as a conversational feature, to let someone else know they had seen their tweet, or to signal agreement. 25 people favorited tweets that made them feel special. Six people favorited tweets but had literally no idea why they did so.