In movies and tv shows the producer is either the person who put up the money to fund the production, or someone acting on their behalf.

How much control they actually have over the production varies, but because they're responsible for the funding they always have an executive veto over anyone else's decision.

An executive producer is just a title that means that a person has more decision making ability than other producers.

So lets say that Warner Brothers is funding a new movie. They'll appoint several of their employees as producers that are each responsible for some area of the movie. IE, one of the producers will be in charge of budgeting for the production of the movie, so that person will be involved in figuring out how much money they're going to spend on specific costumes and sets. You'll have the same thing for marketing and other aspects of the movie, where there is a producer who is working through the small budget details on their assigned area.

They'll then assign an executive producer that oversees the budget for the entire movie without necessarily getting into the level of detail that the other producers are.

In other industries producer can have different meanings, though its typically related to controlling a budget or allocating time.