This indicates the file contains multiple audio tracks (often several different languages).

This is the first segment of a compressed archive.

Here is a quick breakdown of what that file name actually means:

Because this is only "Part 1," you won't be able to open or play it on its own. You will need to download all the subsequent parts (Part 2, Part 3, etc.) into the same folder. Once you have the complete set, you can use a program like WinRAR or 7-Zip to extract the actual video file.

It looks like you’ve come across a piece of a larger archive, likely a high-definition video file split into multiple parts for easier sharing.

This is the "tag" for the release group that encoded and uploaded the file.

This is usually a shorthand code or abbreviation for the title of the content.