An administrator is the person in charge (i.e. the owner or the Bose of the site).
A global moderator is like the manager who helps run the whole site and makes sure the rules are followed.
A moderator is someone who looks after one or more forums assigned to them and to see that the rules are followed.
An internet forum or message board, is an online discussion site where people can hold conversations in the form of posted messages.
The forum or message board is made up of many parts.
1) A category is just a special type of forum or section that cannot be posted in.
2) A forum is a section or sub-forum that is part of a category and can be posted in.
3) Sections, sub-forums and forums are normally just called a forum.