A sub-account or team is an entity grouping several users under a brand, a name, a logo and a domain name for example. In other words, it could be -depending on your situation - another organization you work at, a subsidiary of your business, a Corporate client account, or another department in your company.
Each sub-account has it's own:
-Look and feel (logo, brand/team name)
-Set of templates
-Group of team members
As an account owner, you'll be able to use the same credentials to access all your sub-accounts