1) A politically correct euphemism used to describe chronic homeless persons.
2)A term used to cast a positive or sympathetic connotation upon the parasitic and unrespectable criminal lifestyle choice of the American bum.
3)A term used to describe habitual abusers of illegal substances and career beggars or criminals with no permanent residence or legitimate source of income.
When some resigns or retires from a job, they are on "eternity leave". This can also refer to someone who has passed away, especially someone who worked somewhere for a long time, retired/resigned, then passed away later.
Oh I'm sorry, you didn't know that Kelly is on eternity leave? She resigned and moved to Hawaii!
With regrets I would like to inform you that my boss is officially on eternity leave. I will never see or hear them again. Ever.