SaaS (Software as a Service) is software delivered over the internet on a subscription basis, with the vendor handling hosting, maintenance, updates, and security. For customer portals, SaaS is the dominant delivery model — vendors like Moxo, Clinked, SuiteDash, Salesforce Experience Cloud, and dozens of industry-specific platforms all sell their portals as SaaS.
SaaS contrasts with on-premise software (installed on customer-managed servers, historically dominant) and self-hosted (you operate it but the software is open-source or self-deployed). For most customer portal use cases, SaaS is the right answer — faster to launch, lower maintenance burden, more secure by default. See Build vs. Buy.