A musical phrase is a short section of music into which the music seems to naturally fall. Often a phrase is four bars long, but shorter and longer ones may occur.
It is an inexact term: sometimes a phrase may be contained within one breath, and sometimes they are subdivided by slurs to indicate their proper punctuation in performance.
The art of phrasing by a performer, whether conductor, singer, or instrumentalist, is often instinctive and is one of the features by which an accomplished performer may be distinguished from one less skilled.
Figure 1: Three short musical phrases.
Also see Lyrics | Contours.