A measure of rhythmic quantity; the organized succession of groups of syllables at basically regular intervals in a line of poetry, according to definite metrical patterns. In classic Greek and Latin versification, meter depended on the way long and short syllables were arranged to succeed one another, but in English the distinction is between accented and unaccented syllables. The unit of meter is the foot. Metrical lines are named for the constituent foot and for the number of feet in the line: monometer (1), dimeter (2), trimeter (3), tetrameter (4), pentameter (5), hexameter (6), heptameter (7), and octameter (8); thus, a line containing five iambic feet, for example, would be called iambic pentameter. Rarely does a metrical line exceed six feet.
The metrical element of sound makes a valuable contribution to the mood and total effect of a poem.
Sidelight: In the composition of verse, poets sometimes make deviations from the systematic metrical patterns. This is often desirable because (1) variations will avoid the mechanical "te-dum, te-dum" monotony of a too-regular rhythm and (2) changes in the metrical pattern are an effective way to emphasize or reinforce meaning in the content. These variations are introduced by substituting different feet at places within a line. (Poets can also employ a caesura, use run-on lines and vary the degrees of accent by skillful word selection to modify the rhythmic pattern, a process called modulation. Accents heightened by semantic emphasis also provide diversity.) A proficient writer of poetry, therefore, is not a slave to the dictates of metrics, but neither should the poet stray so far from the meter as to lose the musical value or emotional potential of rhythmical repetition. Of course, in modern free verse, meter has become either irregular or non-existent.
Sidelight: Generally speaking, it is advisable for poets to delay the introduction of metrical variations until the ear of the reader has had time to become accustomed to the basic rhythmic pattern.
Sidelight: In music, the term, rubato, refers to rhythmic variations from the written score applied in the performance.
(See Common Measure, Scan, Scansion)
(See also Accentual Verse, Quantitive Verse, Syllabic Verse)

This definition is in context to Poetry. See more contextual defintions for Meter Or Metre.