- ここで使われている deep は、副詞。"two deep" や "three deep" という形で使い、「2/3列（段／層）に〜する」という意味になる。（if things or people are two deep, three deep etc, there are two, three etc rows or layers of things or people／if people or things are two deep, three deep etc, there are two, three etc rows of them behind or on top of one another／In a specified number of ranks one behind another）
- People were standing four deep at the bar.
- They parked the cars three deep [=three cars in a row], and our car was stuck in the middle.
- People were standing three deep at the side of the road to watch the procession. ※procession：行列、行進
- They were standing three-deep at the bar.