Microsoft CAL Vs Microsoft Volume License

Hi there,
I am wondering if there is a difference between Microsoft CAL Vs Microsoft Volume License.
I am using a server based computing and this info would be a great resource.
I know MS CAL is needed for a software if that software is being installed in the Server end and will be accessed by the clients.
And volume license is a sort of volume license and has certain levels.
But is 5 MS CALs is a Volume License up to 5 users?

Thanks,
Tom