Accounts teams are the teams with user who work together on accounts.
Setup > Customize > Accounts > Account Teams
Enable Account Teams
Enable > Account Teams > Save
Select page layout for which you want to add Account Team Related List.
Account Team enabled. You can Team Roles, Replace Team Roles and Disable account Teams. When the Account Team Role is disabled then related list from all page layouts will be removed.
Account Team related list added to the account page layout.