"Handpan" is the correct spelling for the musical instrument that was created by PANArt in the early 2000s. It is a type of percussion instrument that is played with the hands and is similar to a steel drum or a hang drum.
"Hand pan" is a term that is sometimes used to refer to the same instrument, but it is not the correct spelling. It is a common misspelling of the term "handpan."
While both terms are used interchangeably by some people, "handpan" is the correct spelling and the term that is widely recognized within the handpan community.