Definition
This idiom suggests that appearances can be deceptive; something that looks attractive or valuable on the surface may not actually be so upon closer inspection.
That new investment project looks very appealing, but remember, all that glitters is not gold.
She soon found that the celebrity life wasn't always as glamorous as it seemed, proving that all that glitters is not gold.
This new restaurant's decor is beautiful, but the food is very ordinary; it's clear that all that glitters is not gold.