Global Address List (GAL)
The Global Address List (GAL) is the address look up feature in Office 365. It contains email addresses for individuals and resources, excluding those that are hidden. Office 365 uses the Global Address List to supply email addresses when you are composing a message or inviting individuals to meetings.
Send On Behalf Of
In Office 365, this permission allows a delegate to use this mailbox to send messages. However, after this permission is assigned to a delegate, the From address in any message sent by the delegate indicates that the message was sent by the delegate on behalf of the mailbox owner.
Sub-Domain
A sub-domain is a domain that is part of a larger domain; the only domain that is not also a sub-domain is the root domain. For example, doit.wisc.edu and engr.wisc.edu are sub-domains of the wisc.edu domain.