In music notation, a dot immediately to the right of the note-head of a certain note indicates that its duration is one and a half times that of the undotted note. For instance, a dotted quarter note lasts one and one-half beats instead of one; a dotted half note lasts three beats instead of two.
A note may also be followed by two dots side-by-side, which indicates its duration is one and three-quarter times that of the undotted note. A double-dotted half note would then last three and one-half beats.