Let's first define search as a service. In brief, search as a service is a type of search that uses a software as a service (SaaS) model. That is why search as a service is also called SaaS search.
SaaS is a way of distributing software in which businesses use cloud-based software hosted by a third-party website hosting provider
. Usually, SaaS implies an on-demand pay-as-you-go service with a monthly (or yearly) subscription that can be canceled at any time.
In contrast to SaaS, businesses may choose to develop their own software that will be hosted on their server. This model requires an IT team that will build the server, develop the software, and constantly maintain it.