Zero-result rate (ZRR) is the share of unique searches that returned an empty result set. A healthy ecommerce store sits below 5%; over 10% means meaningful revenue is leaking out of the search box. Every zero-result query is a shopper who declared intent and got nothing.
The biggest causes are: typos (fix with Did-You-Mean), missing synonyms (fix with synonym mining from search logs), out-of-stock filtering (fix by showing the product as “out of stock — notify me” instead of hiding), and overly strict matching (fix with looser tokenization or fallback to fuzzy match).
Track ZRR as a dashboard alongside top zero-result queries. The top 20 queries usually account for half of all zero-result events; fixing them by hand is often a one-afternoon win that recovers a measurable percentage of revenue.