Prospective customer. A person (or business) who is not currently your customer but who may, if conditions are favorable, become your customer. They are at the start of your Sales Funnel, movement through which will "qualify" them into being your customer (or disqualify them, in which case they are no longer of value to your business.)
My book "Choose Your First Product" is available now.
It gives you 4 easy steps to find and validate a humble product idea.