If you’d like a explaining the concept hypothetically, here it is:

If you grew up in the era of Napster, LimeWire, or MegaUpload, you’ve seen a text file named password.txt accompanying a downloaded .rar file. The "Full Pack Password" phenomenon exploded between 2005 and 2015 for several key reasons:

In less ethical corners of the web, it refers to a "full pack" of leaked credentials or personal documents.