1. The place where hammers live. Often an unseen, extradimensioal space just big enough to store one large wooden mallet, used to hit perverts over the head. From anime.
2. Any such hidden location where an object, usually violent in nature, comes from unexpectedly
1. "Did you see Akane? Kuno was getting gropy and then out of hammerspace he got whacked on the head by her mallet."
2. "These action movies are too unrealistic--everyone has hammerspace."
The infinite amount of space within something in which items are stored. Inventories in video games are a prime example, as the character is somehow able to hold a metric fuckton of stuff without any sign of even a bag on him.
Guy 1: "Dude, 500 pokéballs?! How do you even fit all of that in one pocket?!"
Guy 2: "It's a hammerspace backpack, bro."