Absolute pitch, also known as "perfect pitch", refers to the ability of a person to recognize the pitch of any note or sound without reference to other pitches.
For example, after playing a note or notes on a piano or any instrument without any signals, if he/she has basic musical training, and has the ability to name the note accurately, then he/she may have absolute pitch.
Absolute pitch is an intonation memory ability that not everyone (or all musically trained people) possess. It is generally believed that absolute pitch is related to genetics or early childhood training (especially developmental stages between the ages of 3 and 7).