Software-as-a-Service (SaaS; pronounced “sass”) used to be quite a clear and simple proposition: rather than purchase and install a CMS, you simply paid a monthly fee and ran your website inside a larger system managed by the vendor. You became one of many customers running their websites inside this same system.
This is known as “multitenant” software. Whereas purchased and installed software is “single tenant” – you are the sole occupant, much like in a single-family home you built yourself – multitenant software is like an apartment building in which many people live.
The purported benefits are quick ramp-up time and no hosting issues. Indeed, the system is already running and just waiting for you, and since it runs on the vendor’s servers, you don’t need to worry about any of the headaches that go along with infrastructure management . SaaS was “cloud” before that term became common.