help:metatags

Metatags are tags that convey information about an image outside of what is visible in it.

For a list of metatags, see tag group:metatags.

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Taken from Rule 34 (https://rule34.xxx/index.php?page=wiki&s=view&id=66542):

Metatags are tags that describe metadata. Metadata is data that conveys information about other data.

So in other words, metatags are tags that convey extra information about an image or video file but not the content of the image or video itself.

This includes things like year of production, provenance (was it a commission, drawthread request, gift art, etc.?), file size, modifications, edits, translations, source, compression, etc.

Example differences between general tags and metadata tags

In each example, notice how the metadata tags are describing something about the general content tags.

Content: text, dialogue, english_text, japanese_text, spanish_text
Metadata: translated, hard_translated, alternate_language

Content: censored, censor_bar, mosaic_censor, novelty_censor
Metadata: decensored

Content: color, pastel_colors, muted_color, colorful, monochrome, greyscale
Metadata: colorized

General tags often mistaken for Metadata
*_background
censor_bar
dated
watermark
signature / artist_name

The basic rule of thumb is that anything you can see in an image is probably not be metadata because if you can see it, then it is probably part of the content. Here are some examples of metadata that still has a visual component.

Image artifacts like jpeg_artifacts or scan_artifacts are visible, but they are still metadata because they are not intentional parts of the composition or content, they are byproducts of compression algorithms or scanning methods. Tags like animated, slideshow, animatic, music_video, and looping_animation are describing how a sequence of images is perceived, so they are also metadata.