Rhyme is the repetition of similar sounds in two or more words, most commonly at the ends of lines of verse. It is one of the oldest and most recognizable features of poetry, serving simultaneously as a structural device, a mnemonic aid, and a source of sonic pleasure.
Perfect rhyme (also called full or exact rhyme) matches the final stressed vowel and all following sounds: moon/June, bright/night. Slant rhyme (also called near, half, or imperfect rhyme) matches some but not all of these sounds: moon/bone, bright/bat. Internal rhyme occurs within a single line rather than across line endings.
A rhyme scheme is the pattern of end rhymes across a set of lines, notated with letters: ABAB (alternating), AABB (couplet), ABBAABBA (Petrarchan octave). The rhyme scheme is a structural scaffold — it creates expectations in the reader’s ear, and the poet can fulfill, subvert, or abandon those expectations for effect.
In much contemporary poetry, rhyme is used sparingly or not at all. When it does appear in free verse, it often arrives as slant rhyme or internal rhyme — a ghost of the formal tradition, felt but not foregrounded.