TLDR on SLI, SLO and SLA.
Service Level Indicator (SLI) measure of chosen characteristic of the level of service.
SaaS
Software as a service (SaaS) is a software delivery model in which a software application is hosted by a third-party provider and made available to customers over the internet. This means that customers do not need to install or manage the software themselves, and can access it from any device with an internet connection.