Crawl budget is the number of URLs Google will crawl on a given site within a given time window. It’s determined by the site’s authority, health, and how efficiently it responds to requests.
Crawl budget matters for sites over about 10,000 URLs. Small business sites almost never hit their limit. Large e-commerce, directory, or news sites can, and end up with unindexed pages when crawl budget gets wasted on duplicates, parameter URLs, or infinite scroll traps.