A pruning poem is a poem that uses rhymes that are prunings of each other.
Each rhyme word is one letter shorter than the rhyme word before. Otherwise, they are the same word. While it is possible to write a pruning poem in couplets or longer, it is most effective when the reader sees the pruning on the page. Thus, George Herbert, who conducted many formal experiments in verse, writes Paradise as a pruning poem.
Pruning could be accomplished by cutting terminal as well as initial letters, but initial position pruning is the more common and noticeable.