Network2/Concept/Capacity

Suppose that Alice is trying to send messages to Bob over a noisy channel like a radio link.

No matter what sort of link they possess, there are only finitely many different messages that Bob might reliably receive from Alice in a single unit of time.

This quantity is the capacity of their link. Link capacity is typically expressed in bits per second or some unit derived therefrom like Mbps (mega-bits per second).