a license is a way for software manufacturers to make sure that bootleg software is not supported. You must have a license(for businesses) to run certain software. This applies when you have say Windows Server 2003. the server has it's own license. You need client licenses to access this software from the workstation pc's. They are called Client Access Licenses(CAL's) and must be bought in order for them to access the server. You need one for each client. and they are not cheap.