"Topside" refers to the upper part or surface of something, usually referring to the highest point or the uppermost area of an object or location. Full definition
To chop Swiss chard, first fold each leaf in half with topside of the green folded inward. (whfoods.com)
You can marvel at the incredible topside scenery of West Papua, sail through waters where so few boats venture and experience some of the most impressive scuba diving in Indonesia... and therefore the world. (Dive-The-World.com)
At one point in the game, a side character who appears to know, or is familiar with my humanoid character, mentions that I'm underground, away from a war that's been going on topside. (nintendotoday.com)