What’s the term for a hash sent early and plain text revealed later?

I think there is a known pattern where you post the hash of a document, e.g. on Twitter, in order to have its time registered. You could then later publish the document and have it accredited for the time of the hash.

I’m sure someone gave this procedure a name. What is that name?

I found trusted timestamping, but that is a thing for digital certificates, which do not come into play here.