A free tool inside Google Ads that suggests keywords and gives each one's average monthly searches and forecasts.
Keyword Planner sits in the Tools menu of a Google Ads account. It has two starting points: discover new keywords, from words or a website, and get search volume and forecasts, for a list you already have. Google says you need a Google Ads account with billing set up to use it.
Its Avg. monthly searches column is Google's average of the searches for a keyword and its close variants, over the months and location you choose, twelve months by default. Google says the historical figures are shown for exact matches only, whatever match type you enter, and that they're rounded, so treat them as a size, not a count.
For a brand, it answers how many people search for your name, and for your name with “discount code”, “voucher code” or “promo code”, each month. The code searches are the ones most brand checks miss. The figure is one of the inputs to the brand bidding cost calculator, and Search Console gives a second view of the same searches from your own site's side.
Google's own help and policy pages first.