Absolute pitch (AP) is the ability based on the fixed association between musical pitch and its verbal label. Experiments on AP identification demonstrated extreme accuracy of AP listeners in identifying pitch, influences of timbre and pitch range, and difference in accuracy between white-key notes and black-key notes. However, contrary to the common belief that AP is a component of musical ability, it was found that AP listeners have difficulty in perceiving pitch relations in different pitch contexts, and in recognizing transposed melodies, as compared to listeners having no AP. These results suggest that AP is irrelevant and even disadvantageous to music. Systematic music training in early childhood seems effective for acquiring AP. Possible genetic contributions to AP are undeniable, but evidence for them is inconclusive. There are several AP-like phenomena that do not reach consciousness: absolute tonality, long-term memory of pitch of repeatedly heard tunes, specific patterns of pitch comparison in the tritone paradox, and fixed pitch levels in speech. Contrary to true AP observed as a pitch naming ability, the implicit AP phenomena are widespread among general population.