A premise is a machine for generating scenes. "A funeral director who is afraid of the dead" produces scenes on its own; "a film about grief" produces nothing, because it names a topic rather than a pressure. The difference is whether the statement contains a contradiction somebody has to live inside.
The strongest premises put two things in tension that are both true. That tension is what makes the second act possible: every scene can test the contradiction from a different angle without repeating itself.
It is not the theme and not the logline. The premise is the situation, the logline adds the goal and the stakes, and the theme is the argument the finished piece makes about it. Confusing them is why development conversations run in circles.
What is the difference between a premise and a logline?
The premise is the situation with a contradiction in it. The logline adds the protagonist’s goal, the opposition and the stakes. A good premise generates scenes; a good logline tests whether they form a story.
What makes a strong premise?
An internal contradiction that somebody has to live inside, stated concretely. A subject is not a premise, and neither is a setting.