Lines that repeat the same first letter or sound are?

Lines that repeat the same first letter or sound are called alliteration.

Here are some examples:

* Peter picked a peck of pickled peppers.

* She sells seashells by the seashore.

* With whimsical words, the writer wove a wonderful world.

Alliteration is a common literary device used to add emphasis, rhythm, and a sense of playfulness to writing.