Office licensing on terminal server

I have a copy of MS Server 2008 R2 running terminal services.

Each user in the company is going to log into the server to do their work over a remote desktop connection. They will all need access to MS Word. It would be much more productive if Word was installed on the server rather than their desktop machines.

This is mainly a licensing question. How do you install word on the server so that 15 users can each use it simultaneously? Please note that Office 365 is not an option for us.

Thanks,

Dave