It's a literary device that adds a musical quality to writing by creating a sense of rhythm and emphasis.
Here are some examples of assonance:
* "The cat sat on the mat." (repetition of the short "a" sound)
* "The old man tried to light a fire in the cold, damp forest." (repetition of the long "o" sound)
* "The waves crashed on the shore, a sound of endless wonder." (repetition of the short "o" sound)
Assonance is often used in poetry and prose to create a specific mood or atmosphere.