Haki (覇気) is a special ability, divided into three main types, that was introduced in the One Piece series by Eiichiro Oda. The series first began serialization in Weekly Shōnen Jump on August 4, 1997. The earliest example of these powers was in in One Piece Volume 1 CH. 1 "Romance Dawn", though many of its early uses have been retroactively attributed as it was not mentioned or named until much later in the series when it became commonplace.
The English translation of 覇気 is ambition, which serves as a more literal explanation of the ability, as those with the most ambition tend to have the highest strength in Haki and more specifically, the third form of Haki which is the only one that cannot be gained through skill but only through birth, is extremely rare in the world but quite prevalent in people of higher status and power.