There is a distinct difference between a Participant and a Team. Get Gosu lets you form a Team, a team is a persistent group of gamers that exists outside of a tournament. There are no ‘roster locks’ on teams so you can add or remove teammates from your team whenever you want to.
You are not, in any way, required to play tournaments with your teammates. You can register for a tournament without even being on a team. You can register for a tournament with anyone that you want to. You can register for a tournament with your teammates, your buddies, your clan mates, or with random strangers.
Suppose that you are a member of a team, but only two of your teammates are online. You want to play a tournament, so you invite your two teammates and two of your buddies to register for a tournament with you. You and your two teammates can register for and play in the tournament with your two buddies without your two buddies having to join your team. Now that the five of you are registered for the tournament together, what do we call the five of you? The five of you are playing together in a tournament, it would make sense to call you a team, but, a team is a separate entity that exists outside of the tournament, so we call you a Participant.
A Participant is a group of gamers that play together in a tournament. By registering for the tournament together, you, your two teammates, and your two buddies have formed a tournament Participant.
Participants are not persistent; a participant only lives as long as the tournament. After the tournament is over, your two teammates remain your teammates and your two buddies remain your buddies; the relationships that exist outside of tournaments (teammates, clan mates, and buddies) are unaffected by who you participate in a tournament with.