A one-man team is a team with multiple players on it whose fate is perceived to be entirely tied to the scoring abilities of one player. Because that player need not actually be male, the term one-person team has also gained currency in recent years. The term is usually mildly derisive, and often implies that the star player would not look as good while sitting next to stronger teammates. These teams cannot usually succeed against well-balanced attacks from multiple good players at the highest levels of either high school or collegiate quizbowl.
Because of the derogatory connotations, and especially the implied insult to the teammates of the "one-man," it is not a good idea to use this term in reference to any team in your tournament when you are the TD or moderator.
If there is literally one person playing at a team tournament, the term "one-man team" or "one-person team" does not apply and the person is instead playing solo.