It looks like this cropped up in July 2017 in response to a discussion around synonymising content-identification and product-identification together. Specifically, SevenSidedDie suggested they shouldn't get synonymised directly together, but could be both synonymised into materials-identification.
It didn't catch on, but its introduction might've just gone unnoticed.
I think we ought to retag these into content-identification or product-identification case by case and let the tag vanish again for now, unless/until we're ready to merge them together.
Aug 7 2018: I've just now removed the tag from those questions and replaced it with content-identification or product-identification.