> I think they call it "greasing"

This is a reference to RFC 8701, which coined the acronym GREASE ("Generate Random Extensions And Sustain Extensibility"), first in the context of TLS.

https://www.rfc-editor.org/rfc/rfc8701.html

(The earliest draft of the RFC dates back to mid-2016, which is likely the first public mention of the term: https://datatracker.ietf.org/doc/html/draft-davidben-tls-gre...)