Website search is the system behind a website's search bar that indexes the site's content and returns relevant results for what a visitor types.
Also known as: site search, on-site search, internal search
Website search is distinct from web search. A web search engine like Google indexes the public internet and ranks documents across millions of domains. Website search indexes one site — its products, articles, documentation, policies, help content and media — and answers questions about that site alone.
The narrower scope changes the problem. A site search engine cannot rely on link graphs or billions of behavioural signals to rank results; it has a comparatively tiny corpus and very sparse feedback. In exchange it has structured data most web crawlers never see: inventory, price, category, availability, entitlements, order state.
Modern website search is expected to cover more than one content type. Visitors do not maintain a mental model of which box answers which question — they type "where is my order" into the same field they used to look for a jacket. Systems that only index products send those visitors to a zero-result page.