What does CAL means in the MSDN license

I want to set a new development environment; I already have licensed windows 7 & SQL server 2008. But there are not development tools, so I settled on buying standalone Visual studio 2012 and TFS , but I cannot understand what does CAL means?. As for most offers they mentioned that I will get the visual studio team foundation server with one Client Access License. So are the number of CALs associated to the number of software developers which will be using the VS and TFS or what does CAL means in my situation?. For example if there are 3 developers and 2 team leaders then do I need to buy 5 CALs?

Thanks in advance for any help.

Best Regards