What It Is
When a search has local intent, like "plumber" or "breakfast near RiNo," Google answers with a map and a short list of businesses above the usual results. The trade calls that block the map pack or the local pack; Google calls these local results. The same listings appear in Google Maps. Local SEO is the work of earning a place there, and it runs mostly through your Google Business Profile rather than your website alone.
How It Works
Google names the three things that decide local results. Relevance is how well your profile matches the search, which is why your categories and your description matter. Distance is how far you are from the person searching, or from the place they named. Prominence is how well known you are, which Google says includes your reviews and rating, the links to your website, and your standing across the web. Google also says that more reviews and positive ratings can help your ranking, and that replying to reviews helps you stand out.
Distance is the one you cannot change. The other two are work you can do: an accurate, complete profile; a name, address, and phone number that match everywhere; a website that backs up what the profile says; and a steady flow of reviews from real customers.
Why It Matters for Being Found
For a business that serves its own neighborhood, the map is often the whole search. A customer who wants a haircut or a furnace repair frequently calls straight from the listing and never visits a website at all. That makes the listing your front door, and it means a business can have a lovely website and still be invisible where its customers are actually looking.