When someone is a leader but they don't have the formal power.

yes

direct leader

An informal team is similar to a formal team, but does not have a rank structure as in; having a leader or someone who co-ordinates as task. All team members in an informal team are equal in every task given to that team..

Managers should attempt to work with the informal leaders to help achieve the aims of the business. This is best done by attempting to ensure that the aims of the informal leader and the group are common with, or fit in with, the aims of the business.