the occurrence of the same letter or sound at the beginning of adjacent or closely connected words.“the alliteration of ‘sweet birds sang’”
It is something in the nature of ” Round the rugged rock the rascal ran” or “Round the rock the rugged rascal ran.”
It also reminds me of several tongue twisters that I used to have fun with as a child :
She sells sea shells by the sea shore.
Betty Botter bought a bit of bitter butter.
Peter Piper picked a peck of pickled pepper.
There were many others but my memory fails me. Can you think of any others ?