Tantek described these as the "lighter" responses -- things short of a comment/reply. "Likes" are fairly universal examples of reactions.
Currently the term "response" is preferred as an umbrella term for referring to likes, reposts, relies, and all manner of other reactions and interactions with another post.
On The Tapestries, reactions include Like, Agree, Disagree, and various emoticons and emoji like <3 and :zap:
npdoty asks "is a citation a reaction"?