A kippah is a type of head covering. A hat or skullcap, resembling a beanie cap, that Jews wear to temple. In some of the stricter denominations, men wear the kippah all the time. Some men, even in denominations that do not "require" it, wear the kippah all the time. It is worn religiously to show humility in the presence of G-d.
Hebrew: כִּפָּה Plural: Kippot
A kippah is also known by the Yiddish name "yarmulke' (pronounced: yamaka).