A PvP guild team is a named, five-player subset of your guild roster that fights together in structured PvP. Each team(s) within a guild must have a unique name, which is chosen on creation. It will have its own rating, and as such, its own place in a new guild-team leaderboard. Fighting as teams will help fuel your guild with the resources it needs to power its guild hall.
Playing as a team also offers a few perks that can be unlocked in your guild hall. For example, your guild anthem can play at the end of a match, should you be victorious. Your guild team will have a rating specific to that team. While you’re playing as a guild team, matchmaking will use this rating over your personal rating.More Information:
https://www.guildwars2.com/en/news/introducing-pvp-guild-teams/