Teams (Japanese: チーム, Mandarin: 队) are what are used to separate members of AKB48, SKE48, NMB48, HKT48, NGT48, JKT48, SNH48, BEJ48, GNZ48 and SHY48 up. By using 'Teams', members can be categorized more easily. Also, instead of the entire group performing a theater show, only one team is assigned to perform. This allows fans to focus on a certain group of members and give the girls days off. Kenkyuusei are sometimes referred to as Team Kenkyuusei, but is not official.
Teams are named after the letters used in their group's name, except for AKB48 Team 4, Team 8 and SNH48 Team X, Team XII. In the case when a Team's name has already been taken up, roman numerals are used to signify which number of letter that team is. For example, both AKB48 and SKE48 have the letter "K" in their names, so instead of forming a Team K in both AKB and SKE, the AKB team is called Team K and the SKE team is called Team KII.
The Teams of SNH48's sister groups didn't follow this order, because they aren't AKB48 sister groups. For example, BEJ48 Team B and AKB48 Team B, but they follow the order of SNH48 actual teams. For example, SNH48 Team NII and GNZ48 Team NIII (Don't confuse with NGT48 Team NIII)
Each Team has their own captain, who may or may not be the Center of the Team. Traditionally, teams had 16 members, but since the Tokyo Dome Team Shuffle, there is no limit to the amount of members that can be on a team.
The only groups that do not use teams are SDN48, Nogizaka46 and Keyakizaka46, where members were separated by using generations instead. Even without Teams, these two groups have their own captains, with Noro Kayo being the SDN48 captain and Sakurai Reika the Nogizaka46 captain. SDN48 was disbanded in 2012, however.
Sometimes, there are special groups made within the AKB48 Group, such as single coupling song groups. An example of this is Team PB or Team YJ. These teams were only temporary and for marketing purposes, the members within them stayed part of their original teams as well. Other temporary teams, such as Team Undecided and Team Unknown, are used when a member is transferred or promoted, but there either is no team spot available, or they haven't been assigned to a team yet.
Currently, a special Team, Team Kaigai is being used for AKB48 members who have been transferred to sister groups abroad.
A list with the current captains of the teams can be found here.