The definition of a gander is a male goose. The definition of a goose is a type of bird, specifically, it is any bird that is a member of the family Anatidae. Male and female goose and gander are spoken of in the plural form as geese.
Geese are also cultivated and harvested by farmers for food. Goose is a traditional dish for Christmas -- the so-called Christmas Goose -- and is available from many grocery stores, such as Whole Foods, during Christmas time.