Pass away= die ( a euphemistic or polite expression)

• He passed away by a massive heart attack at his house.
• He amassed a lot of wealth, but unfortunately he passed away even before he could enjoy a bit of it.
• His unexpected passing away last year left the poor family in great shock and tragedy.
• He is afraid he won’t be able to pass away peacefully because of his family problems.

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Pass out = (1) to become unconscious for a short time; faint.

• He was hit down by a bike and he passed out at the spot.
• In Delhi many people passed out from the heat wave.
• Several girls passed out and had to be carried off the field.
• (2) pass out (of) – leave a college etc having passed one’s examinations.
• Neethu Sunny passed out from Sahrdaya Engg College in the year 2010 and presently working as a Software Engineer in Cognizant.
• Tomi passed out from Federal College in the year 1978 and worked in Federal Bank for a couple of years and opted out to work as a Sergeant in Chicago Police.

Passing out ceremony /parade  – a function especially for cadets who have completed their training.