People in general, or a group of people; can also mean your family or parents informally.
From Old English 'folc,' from Proto-Germanic 'fulka-.' The word originally meant a tribe or nation, then broadened to any group of people, and by 1800s came to mean people in general or family members in an informal, warm way.
Calling your parents 'folks' instead of 'parents' is specifically American and relatively recent (last 150 years), showing how a formal word can become intimate through generational change—linguists see this as language evolving to match how communities actually relate!
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