serverless just means that a hosting company routes your domain to one or more servers that hosting company owns and where they put your code on. And that hosting company can spin up more or less servers based on traffic.. TL;DR; Serverless uses many many servers, just none that you own.
More specifically: no instances that you maintain or manage. You don't care which machine your code runs on, or even if all your code is even on the same machine.
Compute availability is lumped into one gigantic pool and all of the concerns below the execution of your code is managed for you.
