Packets and links
Latency and bandwidth are not the same number
Two ways a link is slow, two different fixes, and one word that people use for both.
A link has two independent costs. Latency is how long a bit takes to get there: it is distance, and no amount of money makes it smaller. Bandwidth is how many bits per second you can put on the wire, so a big packet takes longer to send than a small one even though both arrive after the same flight.
The distinction matters because the fixes are opposite. A slow because latency problem is fixed by making fewer round trips. A slow because bandwidth problem is fixed by sending fewer bytes. Doing the second when you needed the first buys nothing at all.