Rafa is an adorable short form introduced to the world by actors Rose Byrne and Bobby Cannavale, who used the name for their second son. Rafael is the Latin cognate of the Hebrew boys' name Raphael, but you don't need to be a Rafael to be a Rafa.

Sounds a bit like a shortening of Rafael or a condensation of Rafaela, but Rafa is a name in its own right.