The term "Nerf" is an acronym that stands for "Non-Expanding Recreational Foam." It refers to a type of foam material used in making toys and other products, such as dart blasters or ball games. The unique characteristic of Nerf foam is its ability to expand upon impact, which helps to cushion the blow when someone gets hit with it. This property makes it perfect for creating safe, yet fun, playthings that can be used in a variety of activities without causing any harm.