Positive reinforcement
Adding something the dog wants immediately after a behaviour, so the behaviour happens more often.
Also called: R+ · reward based training · clicker training
The technical definition is narrower than the everyday one: reinforcement is defined by its effect, not by intent. If the behaviour is not increasing, whatever you handed over was not a reinforcer for that dog in that moment, however much you meant it kindly.
This is why food is used so heavily and why it is not bribery. Bribery comes before the behaviour to persuade a dog to do it; reinforcement comes after it to make it more likely next time. And food is used because it is fast, repeatable and works on a dog too worried to care about a tennis ball.
For most household problems the reinforcer that eventually matters is not food at all — it is being allowed to sniff the lamppost, or greet the person, or go through the door.