which term describes a brief reference in a text to a fictional or historical story, person, or event that readers will be familiar with?

Reward is synonymous with positive reinforcement only

If you mean how the great lakes formed, then  the great lakes began to form at the end of the last glacial period 14,000 years  ago, ice sheets  retreated, which led to exposing the basins they had carved into land which then filled with melt-water.