Likewise "CAL" might represent a client access license, but only a licsensing expert knows it.
I get a fair number of questions regarding the CAL requirements of the Team Foundation Server Workgroup Edition compared to the full blown, unlimited product. Here is the best explanation I have seen so far (Thanks to Ajay S.):
TFS Workgroup Edition is not licensed on a Server/CAL model. This means CALs are not required when using the Workgroup Edition. For this reason, the Workgroup Edition does not include any CALs. TFS Workgroup Edition can be used by 5 unique users using any client (MSSCCI, 3rd party client, VS Pro, Team Edition, Project, Excel, etc.).
Once you grow beyond 5 users, you’ll need to upgrade to TFS Standard Edition, which is licensed on a server/CAL model. This means that you must make sure all users have the necessary CALs in place.
A Hitchhiker's Guide to Team Foundation Server Workgroup Edition
Team Foundation Server with SQL Server Technology
Ordering Team Foundation Server