Word of the Day:

: a word that is treated in pronunciation as forming a part of a neighboring word and that is often unaccented or contracted

In "what's happening?" the "s" in "what's" is a clitic.

We hear clitics every day in sentences like "This'll be fine" and "C'mon over here." There are two kinds of clitics: "enclitics" and "proclitics." An enclitic is a clitic that is associated with the word that comes before it. Contractions, such as the "ve" in "would've" and the "ll" in "it'll," are enclitics. A proclitic is associated with the word that follows it. Proclitics are transcribed into print far less often than enclitics are, but we hear them frequently in speech. For example, the sentence "They love to dance" is typically pronounced with the "to" truncated to a "t" that gets tacked onto the front of "dance."