What does "service level test" stand for?

I'm learning about Continuous Integration and Delivery, and I've seen (concretely in this image), that there's a type of test called "service level test". I thought that was it could be something like load tests, but then I saw that actually that was a different concept.

So, my question is, what does "service level test" stand for? What does it test and how? Which are the most popular tools for this kind of testing?