dinner is served
Dinner is ready and literally is being or has been brought to the table or place where it will be eaten. Typically said as an invitation to others to come and eat. A: "All right, everybody, dinner is served." B: "Wow, this all looks delicious!"
Dinner is served.
It is time to eat dinner. Please come to the table. (As if announced by a butler; often jocular.) Sue: Dinner is served. Mary (aside): Aren't we fancy tonight? "Dinner is served," said Bob, rather formally for a barbecue.