The share of ad clicks, or visits, that end in a conversion such as an order: in Google Ads, conversions divided by ad interactions.
Google Ads defines conversion rate as the average number of conversions per ad interaction, shown as a percentage. For a search ad an interaction is a click, so 300 orders from 10,000 clicks is a 3% conversion rate. Google notes that it can go above 100% if you track more than one conversion action, or count every conversion after a click rather than one.
What counts as a conversion is the advertiser's choice: an order, a sign-up, a call. For a sum about sales, make sure the conversion is the order, counted once per click. GA4 and your network each have their own version, over sessions or clicks, and each will give a different figure for the same weeks.
Searches for your own name usually convert far better than generic ones, because the person typing it has mostly chosen you already. So use your brand campaign's own conversion rate, not the account's average, when you work out what a share of brand clicks is worth. The brand bidding cost calculator leaves it blank for you to fill in for that reason, beside your average order value.