The simple answer is that each licensed seat of Keyman Desktop is for a single computer. When you purchase Keyman Desktop, you will find a 'seat count' included in the licence details. A standard licence includes one seat, which should be used on one computer. If more than one person uses the same computer, you still only need a single licence - except in Citrix, Terminal Services, or similar environments.

For a more detailed answer, and answers to other licensing questions, see: Licensing Information