: This is likely a descriptive tag for the content. Given the "4K" label, it often refers to high-resolution video footage or assets intended for Ultra HD projects.
: All parts must have the exact same name except for the trailing numbers. Do not rename them manually unless they are inconsistent. BT-4K.7z.003
This blog post explains how to manage split archive files, specifically focusing on the BT-4K.7z.003 file format. Dealing with Split Archives: A Guide to BT-4K.7z.003 : This is likely a descriptive tag for the content