What search volume means
The figure answers one very specific question: how many people type a query in a given period. It says nothing about who types it, with what intent, or whether that person will end up buying anything. A term with high demand can be irrelevant to a business, and another with minimal demand can carry half the revenue.
It is worth separating it from two other metrics it gets confused with daily. Search Console impressions count how many times a link to your site appeared in front of a user in the results, so they measure your presence and not total demand. Clicks count how many of those appearances ended in a visit. The same query generates a single search, but spreads impressions across every site that appears on the results page.
The difference in definition explains why the three figures never reconcile. Volume covers all users in a location, whereas impressions only record the cases where your page was in the game at all. Their counting also has its own rules: when one and the same result block links several times to your domain, Search Console records it as a single impression.