Hi Jassu,
Admin is your local admin role for your instances. ServiceNow has Admin role too.
System is a system role used by ServiceNow.
Guest is someone who sends an inbound email, and they are not found in the user list. If configured, they use a guest role and are added to you user table.
Glide.maint accounts are used by ServiceNow, just at they have the "maint" role.
