Depending on where you found it, it likely serves one of these purposes: 1. Official Game Patch (v1.2)
In the context of the FreeSpace Source Code Project (SCP), "pieces" or specific ZIP files are used to modernize the game: File: FreeSpace.2.v1.2.zip ...
Knowing the context will help me give you the exact steps to use that file. Depending on where you found it, it likely
: It fixes various bugs and is required for many modern source code enhancements . Depending on where you found it