A team

Noun

 * 1)  The best of a set of teams in a single club.
 * The A team are playing away this Saturday.
 * 1)  A group or team which performs its work most effectively; a very good team.
 * It looks like the A team are on duty tonight - I've never seen the hall cleared so quickly!
 * 1)  A country's reserve team or development squad, comprising the best players not selected in the national team.
 * He was then selected for the South African A team before making his international debut… 
 * NSW all-rounder Moises Henriques has been named captain of the Australia A team to play England in Hobart next week. 

Usage notes
In sports, teams are often labeled A team, B team, C team, etc. or 1st, 2nd, 3rd. For the informal usage, B team instead most often refers to a team or group who do subpar work, often in direct contrast to a supposed better A team.