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$ is the shell prompt; he's not typing it. "3 millilightseconds" is the distance light travels in 3 milliseconds, the time a "zero" timeout would take to actually timeout. (This comes directly from the definition of the lightsecond: how far light travels in one second) "miles" is what he wants to see that distance converted to. Turns out it's 558 miles; one mile is 0.00179 of 3 millilightseconds.

Point Of Presence (POP) is the location where two or more networks meet each other to connect.

Here is a good explanation: https://blog.stackpath.com/point-of-presence/

Point of Presence is where the university network would connect with the internet

POP I believe is "point of presence"; I believe its meaning is "the point at which our network connects to the internet".