Park admission is required for in-park dining. Just to be clear, you must have valid theme park admission and a Disney Park Pass reservation at the location of your meal.

It depends entirely on where the restaurant is located. If the restaurant is inside one of the four main theme parks (Magic Kingdom, EPCOT, Hollywood Studios, or Animal Kingdom), you must have a valid park admission ticket and, depending on current rules, a park reservation for that day to enter and dine. However, many of Disney’s best dining experiences are located at the Disney Resort hotels or in the Disney Springs shopping district. These locations do not require any park ticket at all. You can book a table at places like Chef Mickey's or The Boathouse and simply show up. This makes resort dining a popular "rest day" activity for guests who want the Disney atmosphere without using a ticket day. Just remember that for in-park dining, having a restaurant reservation does not grant you free entry to the park; you still need to pay for admission to get to your table.