The most common interpretation is a compressed file for a specific software version, where "4.2" is the version number and ".7z" is the 7-Zip compression format .
In rare cases, "7Z" appears in scientific research as part of a chemical isomer or molecular name. 4.2.7z
You might be looking for a specific download like ogl-samples-4.1.4.2.7z (OpenGL samples) or HPM_v0.4.2.7z (a game mod). The most common interpretation is a compressed file