Twitter has announced that will change the star icon normally used for adding a tweet to your favorites list of tweets and replace it with a like icon in the form of a heart. The change is prompted by the ambiguity often caused by the star icon. Often newer users of Twitter don't intuitively know that a star means that they are favoring a tweet.
This often leads to users favoring tweets later on in their Twitter learning curve or never using the feature at all. Twitter says "You might like a lot of things, but not everything can be your favourite" when explaining why they are undertaking this change.