On sites like 123mkv, a "Repack" typically refers to a video file that has been re-encoded or re-packaged from a higher-quality source (like a Blu-ray or high-quality web rip) to meet specific criteria:

What is Hollywood Repack?

One Tuesday, a highly anticipated sci-fi epic was released digitally. Within minutes, Elias had the raw file. He didn't watch it for the plot. He watched the "bitrate peaks"—the scenes with heavy rain, explosions, and flickering lights that usually turned into a blurry mess of pixels when compressed.

Using 123mkv.com is straightforward: