What are upstream and downstream USB ports? THANKS.

[UKspace]

I am thinking of getting a monitor with built-in USB ports. On the specification, it states that the monitor has two upstream and two downstream USB ports.

What is the differece?

 

[Gunbuster]

One looks like the one on webcams, mice, KB (plugs into computer upstream) the other one looks like the end that plugs into printers and such (plugs into device downstream)