"Peter Piper" is an English-language nursery rhyme and well-known alliteration tongue-twister. It has a Roud Folk Song Index number of 19745.
Illustration from Peter Piper's Practical Principles of Plain and Perfect Pronunciation (1836 American ed.)
Alliteration is the repetition of syllable-initial consonant sounds between nearby words, or of syllable-initial vowels, if the syllables in question do not start with a consonant. It is often used as a literary device. A common example is "Peter Piper picked a peck of pickled peppers," in which the "p" sound is repeated.
Gilbert and Sullivan's comic opera The Mikado contains a well-known example of alliterative lyrics: "To sit in solemn silence in a dull, dark dock, In a pestilential prison, with a lifelong lock, Awaiting the sensation of a short, sharp shock, From a cheap and chippy chopper on a big black block!"