What it is
A practical definition
Reranking is the second selection pass, where the system lifts the best-fitting options to the top of an already retrieved set.
Example in ecommerce
After the first retrieval step the assistant can reorder results so the products that match both the request and the business rules come first.
Business impact
Raises the quality of the top positions, which drives CTR, product page visits and the odds of a purchase.