The jitters are that shaky, nervous feeling you get before something big — a test, a match, a talk, a wedding. You have the jitters, or you get the jitters. The word is almost always plural, and it often takes the, like the flu. Coffee can give you the jitters too, a jumpy, over-awake kind of nervous. Informal. Younger and older people both say it. Though actually, a single shake is not “a jitter” in this meaning; the feeling comes as a set.