The identifier appears to be a specific, often viral, video file name or a cryptic code used in niche online communities (such as TikTok, Reddit, or Discord) to refer to a particular piece of "lost media," a meme, or a specific short-form clip .
Best for Reddit or X (Twitter) threads exploring the "mystery" behind the file. The Mystery of 21323.mp4: Explained.
This style works best for TikTok or Instagram Reels where you want to spark a "lore" discussion in the comments.