Region: General | Usage example: He went for a run after work just to blow off steam.

Blowing off steam

Meaning

Releasing built-up stress or frustration.

Used for physical or emotional outlets that help someone calm down.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

Boilers needed to release steam so they would not explode, a vivid industrial metaphor.

Industrial era writers turned the literal vents into a mental-health metaphor.