A phrase mark, better known as a slur, indicates that a passage of music should be played legato. Legato is an Italian word meaning smooth. Phrase marks play a significant part in musical shape. It is usually placed on the note head side in order to avoid crossing over note stems.

A phrase is a section in music that express a complete idea. For example, in classical music, phrases are usually symmetrical in length. For music that is written today, a phrase can be any length. The purpose of a phrase mark is to define sections expressing complete ideas.

A phrase mark is often called a slur. It defines a group of notes, within a phrase, to be played legato. It is properly balanced with other articulations to bring musical expression to its fullest.

For bowed instruments, a slur indicates one continuous motion of the bow for the duration of the slur. The bow changes direction at the end of each slur and articulation.

In vocal music, slurs group notes under one syllable. The slur ends at the change of all syllables. Slurs are mostly used when notes, such as the quarter note, half note and whole note, can not have beam groupings.