Greg used the term precisely and correctly – his post describes taking a general zero-knowledge proof feature and using that to produce actual covenant constructions where a coin and all possible spends of that coin are permanently constrained in a particular way, creating a burn address that allows the burnt coins to be burnt again and again:
A particular sort of rule could take the form of requiring any output scriptpubkey to be of the form
THIS_VALIDATION_KEY && {whatever rules you want}and by doing so you have effectively created a coin which is forever subject to a covenant which will run with the coin and forever constrain the use of it and its descendants degrading and its fungibility.