Admin - short for "administrator". In teams admins have the highest position and power of control. Admins are allowed to create new posts and modify their own or other people's posts.
E.g Michelle posts "I love XXX"
As an admin - you can change it to -
"I love YYY"
In addition - admins can change the template/design, and also change blog settings.
The other position is guest - guests are normal members who can only create posts and modify their own posts only. They cannot mess with the template or blog settings.