The legal term is "reasonable articulatable suspicion". Reasonable suspicion is evaluated using the "reasonable officer" standard, in which said person in the same circumstances could reasonably believe a person has been, is, or is about to be engaged in criminal activity. Such suspicion is not a mere hunch.

Neither is DWB (driving while brown), which is what the stops the OP is experiencing boil down to.

That's the legal theory, anyway. In real life, PC and RAS are whatever the cop says it is, unless you've got a real stickler for a judge. Most judges give law enforcement a wide latitude of allowable judgments, in most cases way too much latitude IMNSHO.