Typically used in discussing different SaaS models. In the Multi-Tenant approach the hosted SaaS application serves the needs of a large number of customers using the same instance of the application, partitioning the data for those customers within the application itself. Sample Multi-Tenant SaaS applications include examples like Dropbox, Salesforce.com, Expedia, and Amazon.com. The alternate approach is Single Tenant, where the SaaS application is a dedicated instance of an application for a specific end-customer, and can be hosted on-premise or through a hosting service like Amazon AWS EC2, Microsoft Azure or others.
See also Single Tenant