Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

[EX Q]: a breed is a domesticated race or type of an animal or plant.
[EX A]: breed

[EX Q]: nightmare disorder, also known as "dream anxiety disorder", is a sleep disorder characterized by frequent nightmares.
[EX A]: nightmare disorder

[EX Q]: la villette, calvados is a commune.
[EX A]:
la villette, calvados