Значения термина use rem на английском

The Verdict: Newfangled alarm clocks may use REM-tracking sleep monitors and sunrise-mimicking lights, but the best wake-up technology was actually perfected 30 years ago.

Mobify's Roman Rudenko has an article on CSS-Tricks that shows how to use REM units to scale specific page elements while leaving others unaffected.

Rudenko even shows how you can use REM units as a replacement for the very powerful, but not very well supported, viewport width unit.