WebM is a royalty-free audiovisual media file format. WebM posts are animated, but the difference that separate them from GIFs and Flash posts is that they use video players.

This tag should be used for submissions that are in WebM format, made more evident as this image board denotes them with "WEBM" on their thumbnails.

See e621:supported filetypes for information on how to encode WebM files to be accepted to the website.

As of April 23, 2025, eSix now also supports MP4 files for videos, not just WebM.