Assonance is a resemblance in the sounds of words/syllables either between their vowels (e.g., meat, bean) or between their consonants (e.g., keep, cape). However, assonance between consonants is generally called consonance in American usage. The two types are often combined, as between the words six and switch, in which the vowels are identical, and the consonants are similar but not completely identical. If there is repetition of the same vowel or some similar vowels in literary work, especially in stressed syllables, this may be termed "vowel harmony" in poetry (though linguists have a different definition of "vowel harmony").

A special case of assonance is rhyme, in which the endings of words (generally beginning with the vowel sound of the last stressed syllable) are identical—as in fog and log or history and mystery. Vocalic assonance is an important element in verse. Assonance occurs more often in verse than in prose; it is used in English-language poetry and is particularly important in Old French, Spanish, and the Celtic languages.