Domain (noun)

1. A field of knowledge or expertise.
2. An area of control or influence.

Origin:

From middle english, from old french domaine, from latin dominium ("property, ownership, control, jurisdiction"), from dominus ("lord, master, ruler").

Examples:

1. He is an expert in the domain of quantum physics.
2. The company's domain is the production of electrical appliances.
3. The domain of the king extended over several territories.
4. The domain of the internet includes all the websites and online services.
5. The domain of the study is the behavior of animals in their natural habitat.