express javascript node.js

Enabling http compression with express

I’m messing around with the Darksky API and under one of the query parameters it states:

extend=hourly optional

When present, return hour-by-hour data for the next 168 hours, instead
of the next 48. When using this option, we strongly recommend enabling
HTTP compression.

I’m using Express as a node proxy which hits the Darksky api (i.e. localhost:3000/api/forecast/LATITUDE, LONGITUDE).

What does “HTTP compression” mean and how would I go about enabling it?