A hop is a computer networking term that refers to the number of routers
that a packet passes through from its source to its destination.
The number of hops from a source to a destination can be determined by using the tracert command from the Command Prompt in Windows.
Note: It's technically more correct to refer to my definition of hop as the hop count. An actual hop is the action that occurs when a packet jumps from one router to the next. Most of the time, however, a hop count is just referred to as a number of hops.
Examples: "On a trace route from my home computer I discovered that it takes 15 hops to reach www.google.com!"