Player character stores abnormally large objects in their pockets or other luggage that should NOT be able to hide them, especially if such pull-out-of-pocket action is shown.
Alternate name: Malletspace
The first video game about Hammerspace was released on October 27, 1988.
Games where player can't see it in action are perhaps not useful here since there's no proof it is actually hammerspace (see walking armory tag though). However, games where it's explained however as something akin to hammerspace are applicable.
Extremely common feature in adventure games where it's done most commonly as obvious hammerspace, in other games it's usually done "behind the screen".