You can have different termbases for different customers.
Example
You are creating a new project and have already created a few TM databases previously. In the Start New Project wizard, you might see something like this:
Termbase Guide
Termbases (1 of 3): Creating Termbases
June 25, 2019
3:27
Termbases (2 of 3): Editing Termbases
2:44
Termbases (3 of 3): Using Termbases
2:02