When someone “passes out” it means that they become unconscious for a short time. This could be from illness, tiredness, heat, emotion or alcohol. Another verb for this is "to faint".

Whats it mean to pass out?

Fainting happens when you lose consciousness for a short amount of time because your brain isn't getting enough oxygen. The medical term for fainting is syncope, but it's more commonly known as “passing out.” A fainting spell generally lasts from a few seconds to a few minutes.

Why do we say passed out?

It means 'to faint' or 'to lose consciousness' for a short time as in these examples: The painter was so drunk that he passed out. He had an accident this morning and passed out.