In short
A limited-access high-speed road, typically 55–70mph; also called a highway or interstate.
A freeway is a limited-access high-speed road in the US, typically with speed limits of 55–70mph. Synonyms include highway, interstate, expressway, throughway.
Most US road tests at urban DMVs include 5–10 minutes of freeway driving — merging, lane changes, exiting.