This refers to a plain text file ( .txt ). In the world of warez and forum archives, a .txt file is the safest, most universal way to share a link. It cannot run malicious code, is readable on every operating system (Windows, Mac, Linux, Android), and is easily hidden inside other files.
Historically, the forum shared "portable" chess software and collections of download links in text files. Users on r/immortalChessForum often discuss how to use these text files, including managing password-protected archives. chess imc immortal chess forum link txt portable