In English, assonance means similar vowel sounds used in groups of words, not necessarily rhyming or following each other, e.g. in "slow motion" the long "o" sounds make the words seem slow.
Assonance is often used for poetic effect. It is a technique similar to alliteration or consonance, but involves the vowels, rather than the consonants. Also, the vowel sounds should be similar, but do not need to be exactly the same. They may also occur anywhere in the word, rather than merely at the beginning or in a stressed syllable.
Poets can use assonance to draw particular words together, or to create particular effects associated with certain sounds. Rhyming words always demonstrate assonance, since in order to have at least one rhyming syllable, the vowel sounds of each word must be the same. Because of this, the technique is also useful when poets create approximate rhyme. Assonance can give the impression that two words rhyme, even when the consonants at the beginnings or ends of their syllables are actually different.
See how well you do in the following quiz all about assonance. Remember that assonance describes how words sound, rather than how they are spelled!