: Often stands for "Initial Technical Training" or "Integration Testing," indicating the environment or stage for which the software was intended.

Article: Managing Multi-Part Archives in Technical Deployments The Challenge of Large-Scale Software Distribution

: You cannot extract part4.rar alone. The extraction utility (such as WinRAR) requires every segment of the set to be in the same directory.

: The version number, suggesting a fourth minor revision of the initial release.