"SaaS" - "Software as a Service" - is a software usage model, when a vendor licenses a software system for use as a service on demand, either through a "pay-as-you-go" model or a time subscription.
SaaS tools is also known as "Web-based", "on-demand" or "hosted software", because SaaS solutions run on the vendor's hardware and it is the vendor who takes care of security, performance, hardware maintenance and availability. It is a software usage model when an online application is being accessed as a service on demand. Nothing needs to be installed "on-premise"
Regarding the CRM Sowftare, this means that rather than purchasing software and hardware to install and run our CRM Software on your own site, you need only a computer/smartphone/tablet with a web-browser to access and use the SaaS CRM.
Benefits comapred to traditional software