a magic charm or amulet
Etymology & Evolution of the Word
The word originated in 1920s America probably as a creole from the Gullah word moco, meaning magic or witchcraft and the Fulani word moco'o, which meant medicine man. As the term was Americanized its usage changed and soon it came to mean a man's charm with women, or vice versa. Mojo was a man's charm, that thing he used when "working his magic" talking to the ladies. Its likely that the word took on its sexual meanings from the "mojo bags" described above. The word today is applied more loosely to mean a person's particular ability to perform well in any area as well as their personal style of doing that thing.
The phrase "get my mojo going" (or sometimes "working") is an example of another usage of the word, similar in many ways to its meaning as charm.
The word is perhaps best known today because of Mike Meyers' character Austin Powers in the film series of the same name who uses the word to refer to his sexual prowess and charm. The plot of the second film in the series revolves around Austin's quest to travel back in time to retrieve his mojo which has been stolen by Dr. Evil.