This almost always refers to "Camera." Depending on the source, it could be for: Firmware: Updates for IP or CCTV cameras.
The "21" in the name often indicates a version number (v2.1) or a specific date/channel associated with the recording or software update. cam 21.7z
This is a "7-Zip" compressed file. It uses high-compression ratios to package multiple files or large data into a single, smaller container. This almost always refers to "Camera