Pinning
Pinning fixes a specific product to an exact position in a results list — for example, always first — rather than just raising its relative rank the way boosting does.
Part of Merchandising
It's the most rigid form of merchandising control: a pinned product stays in its assigned slot regardless of query relevance or other ranking signals, which makes it useful for guaranteed placements but risky if overused, since it can push more relevant results further down.