Scalability is the ability of a system, product or business to handle more work, more users or more customers without breaking, slowing to a crawl or needing costs to grow just as fast. A scalable setup can grow by adding resources in a planned way instead of being rebuilt from scratch.

Cloud vs on-prem is the choice between running software and data on servers rented from a provider over the internet (cloud) or on hardware a company owns and operates in its own building or data center (on-premises). The decision shapes cost, control, security responsibilities, speed of setup and who fixes things when they break.

SaaS, short for software as a service, is software you use over the internet and pay for on a subscription, usually per user per month or per year. The provider runs the servers, handles updates, security and backups, and you simply log in through a browser or app instead of installing and maintaining it yourself.