Folkfact

The term folktale refers to a story passed down from one generation to the next.

I suggest the creation of a new term: folkfact.

A folkfact is a fact that is handed down through generations. The accuracy of a folkfact is often not questioned, and its origin is unclear.

Examples:

Rusty objects cause tetanus

Mongol warriors, knowns as Tartars, invented steak tartare by tenderising meat beneath their saddles.

Folkfacts are similar to common misconceptions, for which Wikipedia provides a comprehensive list.