The repetition of the same initial consonant sound in neighbouring words is called alliteration.
Alliteration is a sound-based literary device: the repeated element is the opening sound of a syllable, not necessarily the opening letter. “Wild winds whistle” uses the /w/ sound repeatedly, while “Peter Piper picked” repeats /p/. This makes phrases more rhythmic, memorable, or emphatic, which is why alliteration appears frequently in poetry, slogans, headlines, speeches, and children’s literature.
Alliteration is not the same as simply beginning words with the same letter. “City and cereal” begin with the letter c but use different sounds, while “funny phrase” can create alliteration even though the spelling differs. Stress and pronunciation can also affect whether a literary analyst considers a repetition truly alliterative.
The broader term consonance covers repeated consonant sounds anywhere in words. Alliteration can be viewed as a particular kind of consonance occurring at the beginning of a syllable. Rhyme usually repeats sounds at the ends of words, as in light and night; assonance repeats vowel sounds, while onomatopoeia uses words that imitate sounds.