Mano-a-mano is a Spanish and Italian construction meaning "hand to hand" . It was used originally for bullfights where two matadors alternate competing for the admiration of the audience.
Current Spanish usage describes any kind of competition between two people where they both compete trying to outdo each other.
Within the Doce Pares Eskrima fighting system, it is one of the three ranges of engagement, specifically the closest one. This does not indicate solely unarmed combat.
This term has been adopted in English with similar meaning, possibly by Ernest Hemingway. The English adoption can be likened to the phrases "one on one", "head to head", or "single combat" and conveys the idea of intense competition.