How does maxWaitingClient work in the generic pool?

Question

Node.js

Is there such a generic pool library?

And there it is written

maxWaitingClients: maximum number of queued requests allowed, additional acquire calls will be callback with an err in a future cycle of the event loop.

The question it means on 1 connection how many requests or it on all connections?
If the number of requests exceeds, will there be an error or will it switch to another connection?