Wig假发（法官、律师在法庭上使用或者用来遮秃）

Definition: A covering for the head made of real or artificial hair, typically worn by judges and barristers in law courts or by people trying to conceal their baldness. [Oxford Dictionary]

Example:

A thick braid of hair hung just above the bench's surface, looking more like a wig than real hair.

Britain's top judges and barristers traditionally wear wigs in their court appearances.

Hairpiece（使头发看上去更长或更浓密的）假发

Definition: A patch or bunch of false hair used to augment a person's natural hair. [Oxford Dictionary] A hairpiece is a piece of false hair that some people wear on their head if they are bald or if they want to make their own hair seem longer or thicker. [Collins Dictionary]

Example:

Depending on the cause and your preference, alopecia can be treated with medicines, surgery, or hairpieces.

Toupee“（男用）小型遮秃假发”

Definition: A small artificial hairpiece worn to cover a bald spot. [Oxford Dictionary]

Example:

There was unkind talk in the press about him dyeing his hair, possibly even wearing a toupee.

I've seen ads for beautiful toupees for as low as $9.95.