This note is a quaver. A quaver has half the length value of a crotchet and a quarter of the length value of a minim. You most often see a quiver as one of a pair, with the curly tail transformed into a straight line joining the couple, or as a triplet or in a set of four quavers.
Alternatively, you may see a quiver on its own following a crotchet that carries a dot after it. This is called a dotted crotchet and is worth one and a half beats, the quaver providing the extra half pound. This affects the music of a vast, short rhythm, or like a man with a limp - long, short.