The practice or advocacy of sexual relations or romantic relationships outside traditional or conventional arrangements.
From hetero- (other, different) plus -icism (a doctrine or system). Related to heterism and heterize, terms developed in 19th-century sociology and philosophy.
This Victorian-era term was invented by serious sociologists trying to describe non-traditional relationships—it's a super formal, academic way to discuss what most people now just call 'alternative lifestyles.'
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