Glossary
Crawl budget
How much of your site a search engine bothers to fetch.
What it is
Crawl budget is the practical limit on how many URLs a crawler will request from your site in a period, shaped by how large, how fast and how useful it judges the site to be.
Why it costs you money
It matters on stores because filters can generate thousands of near-identical URLs. A crawler spending its budget on colour-plus-size permutations is not spending it on the product pages you want indexed.
How to check it yourself
Check Indexing → Pages in Search Console. A large "Discovered — currently not indexed" group on a big catalogue is the classic symptom.
Where this matters