This is called sidechain compression. Sidechaining is a technique where the audio signal of a track is used to trigger a device - theoretically it can be used in a number of ways, but the vastly most popular and well-known application is with compression – basically the bass drum hit is being used to "activate" the compressor, which then pushes down the level of the track(s) it's on. If this sounds complicated, you can just think of it as volume automation for the rest of the tracks, excluding the bass drum.