Metadata is data about data; from the dictionary: a set of data that describes and gives information about other data. The smallest element you can resolve is pure data, everything else is metadata.

Any jurisdiction claiming its interest lies only with “metadata” can almost certainly make a case for anything of interest being metadata.

Given a collection of words representing an email message, it could be argued the relationship of one word to another is metadata. Maybe each word would engender two items of metadata: “word preceding” and “word following.” It is hardly a stretch to reconstruct the original data—or email message.

Another example might be a transcript of a voice call. The call represents the data; the transcript represents metadata. Again, you could argue storing the voice call recording on a hard drive or in memory represents a metadata representation of the original audible voice. Magnetic data about the original sounds—metadata.

Metadata is slippery.

I would go as far as saying any information is metadata.

Without a strict legal definition of metadata—or some more appropriate word—to describe the point at which metadata stops and data starts I would argue it is unsafe to use the word metadata in any legal context.