To be coachable means to allow yourself to be coached: accept criticism, want to improve, do the necessary extra work in order to perform better, listen to the coach. Critical feedback – regardless of how clear, fair, diplomatically communicated – is only helpful if the team member is willing to work with the coach.
When judging talent American sports coaches look carefully at the willingness and ability of a player to be coached, their coachability. American managers are no different. The ideal player (employee) is one who is self-critical, identifies their own weaknesses, takes the initiative by looking for ways to improve, and communicates all of this to their boss.
American team members want a team lead who can coach. American managers want employees who are coachable.