Multitenancy in cloud computing refers to sharing the resource pool among different tenants. The computing power and memory are shared while data is isolated, and only the owner can access it. The customers in a multitenant environment are agnostic of each other.
In SaaS (Software-as-a-service), multitenancy refers to the ability to have one application that serves multiple users. The data remains isolated between the customers while the access to the application is the same for everyone.