What does "in-flight request" mean for a web browser?

Question

I'm trying to decipher the meaning of "in-flight request" in the context of a browser loading a web page:

Look for the first interactive window where there is a contiguous period of 5 seconds fully contained within the interactive window with no more than 2 in-flight requests

Is it referring to HTTP requests? If so, what's the difference between an in-flight request and any other kind of request?

Answer 1

An in-flight request is a request that has been started but not yet completed, a.k.a. a request in progress.