Asking because of this line: "Jin (Su): At 1st level, a sha’ir learns how to contact a jin—a minor, insubstantial genie that makes its home on the elemental planes."
Insubstantial's definition in this case means 'weak' or 'lacking substance.' Think like a piece of twine; it has a shape and you can interact with it, but it will break with a little stress.