What is SaaS ?

SaaS or Software-as-a-Service, just as the name indicates its basically a simple program or software given as a service.

or you can put it this way:

Software given to a bunch of users for a price to get a useful service done for a specific period of time. This is the definition I find in all the profit making saas products.

A SaaS product should contain

1. A useful service
2. Specific period of time (this can even be a lifetime)