Here's a breakdown:
* Focus on vowel sounds: Assonance focuses specifically on the *sound* of the vowels, not the letters themselves.
* Within a phrase or sentence: The repeated vowel sounds need to occur close enough together to be noticeable, typically within a single line of poetry or a short sentence.
* Musical or rhythmic effect: Assonance adds a sense of flow, rhythm, and even a bit of "sing-song" quality to writing.
Example:
"The sea shells sparkled on the shore."
Here, the repetition of the short "e" sound in "sea," "shells," "sparkled," and "shore" creates assonance.