What's "ball pit"? How does it look like?
Native speaker’s answer
Rebecca
As you can see in the video, a "ball pit" is a pit (or lowered area of the floor/ground) that is filled with toy balls. In this video, Sheldon is playing in a children's ball pit. Ex: It is easy to lose things in a ball pit, as it's filled with balls. Ex: I lost my son in the ball pit.