A tenant is your company's account with LMS. Normally we'd call this an "account" or "user," but both of those terms refer to something else in the software. Additionally, any number of agents can be users with the same tenant — they all share the same credentials to use the API.
Each tenant has its own database. Your data is your own, and no other LoanPro customer can access it. A single company can have more than one tenant inside LoanPro.