You know you can just define individual words to figure out what things mean, right? Like so:

Alternative: another option or substitute for the usual or original thing.

Frontend: the user-facing part of a website or application that people interact with.

Instances: separate running copies or deployments of a service or application.

Could: indicates possibility; something is able or potentially able to happen.

Host — to run, provide, store, or make a service available on a server.