SaaS (software as a service) is software you rent rather than own: hosted by the vendor, used in the browser, billed per month or per seat. It trades control for convenience — instant start, no maintenance, but your processes bend to the tool, prices rise per employee, and your data lives on someone else's terms.
The honest arbitration: SaaS for solved, generic problems; custom for the process that is your edge. The full grid is in custom CRM versus SaaS.