12

Numbers:
* A dozen
* One score

Time:
* Noon
* Midnight

Measurement:
* Inches in a foot
* Pounds in an ounce
* Quarters in a dollar

Religion:
* Number of apostles in the Bible
* Number of tribes of Israel

Literature:
* Number of labors of Hercules
* Chapters in the book "The Odyssey"

Music:
* Number of chromatic semitones in an octave
* Number of notes in a whole tone scale

Other:
* Number on a standard die
* Age at which children can legally drive in many U.S. states
* Number of zodiac signs