What is alliteration and what are alliterative words?

Alliteration is the repetition of a sound. So, for instance, the sentence "Sally sells sea shells by the sea shore" repeats the sounds of both S (sss) and SH, which is why it is a tongue twister. It is hard to say it correctly quickly many times in a row because we tend to make all the sounds the same. Another example would be "Tommy tends the turtle." There are a lot of T sounds, and so it is alliterative, repeating a specific sound. Alliterative Words are just Words used in an alliteration.