• something that is not out of the ordinary or unusual;
• something that is familiar to the masses;
• something that belongs to an identifiable genre, such as detective fiction, horror, fantasy, or science fiction.

See also normal.

Antonyms

• underground (culture),
• off-beat,
• eclectic (although an improper use of the term),
• avant-garde,
• special (in the context of education, where it is often used as a verb).