Toad Square is a location inside Bowser's body that appears in the game Mario & Luigi: Bowser's Inside Story. This is the main area inside Bowser where Mario and Luigi can go to buy items and heal up their HP and BP. Toad Square is located directly in the middle of Bowser's body and is located to the left of the Challenge Node.
After escaping the Trash Pit, Mario and Luigi venture to Toad Square where they meet up with Toads that decided to set up a settlement inside Bowser's body. Mario and Luigi stock up on items and heal up if needed and venture of further into Bowser's body.