A bachelor pad is a home (pad) in which a bachelor or bachelors (single men) live. In the United States, it generally refers to small houses or apartments where unmarried men, often college/university students, live until they obtain larger or more luxurious houses or apartments, are married, or generally "move up" in standards of living and taste. It also became a symbol of independence and freedom for young people when leaving their parents' house for the first time.

Source: Wikipedia