Alliteration is a literary device in which a series of words in a sentence or phrase begin with the same consonant sound. This technique is often used to create rhythm, enhance mood, or emphasize particular ideas. For example, in the phrase "Peter Piper picked a peck of pickled peppers," the repetition of the 'p' sound creates a catchy and memorable effect. Alliteration is commonly found in poetry, tongue twisters, and brand names.