Thus, the file literally means: Sonic & Knuckles with Sonic 3 attached, binary format.
If you are writing or looking for a paper involving this file, it likely falls into one of these categories: Emulation Research: sonicknuckleswsonic3bin game file
Whether you are playing for the music, the speedrunning tech, or the nostalgic trip to Mushroom Hill Zone, this is the version that keeps the community alive. Thus, the file literally means: Sonic & Knuckles