The Google Ads setting for where a campaign's ads may show: countries, regions, cities, postcode districts or a radius, with exclusions.
Every Google Ads campaign targets one or more locations. In the UK that can be the whole country, a region, a city, a postcode district (the first half of a postcode, such as M1) or a radius around a point. Any listed location can also be excluded, so a campaign can target the UK and leave out London.
Google works out where a searcher is from signals such as the IP address. Its location options decide who counts: the default reaches people in, regularly in, or interested in a targeted place, while the narrower option reaches only people in or regularly in it.
For brand searches this means a results page is local. An advertiser can show in Manchester and not in London, or everywhere except the city your office is in, for an ordinary reason such as a delivery area. Campaigns can also exclude IP addresses, up to 500 per campaign, which can include an office's public address. A clear page from your desk proves only that the page was clear there.
Ad preview and diagnosis lets you set the location, and Not where you are goes deeper.
Google's own help and policy pages first.