It is a Yarmulka in Yiddish. However, it is most often called a kippa, which is Hebrew. It is worn as a reminder that Hashem is above you at all times.
Usually, the skullcap is worn during worship, but the Orthodox Jews wear them at all times as a sign of respect to God. Incidentally, the Hebrew word for this is Kippa and in Yiddish it's known as a...
The kippah is the Hebrew name for the skull cap that Jewish men wear and the majority of Jews use this word. Another name would be yarmulke, which is Yiddish. It is used to show respect to God as...
Differences in hats are usually the result of regional variation and ethnicity within Judaism. The wearing of hats is not a law, but it is a custom with the force of a law.