I've been working on some vintage electronics lately. In the course of this work, I've found that in some cases it is much easier to design a circuit to replace an old DIP chip that has failed than it is to locate the old part. (Actually, the bigger problem is that some of these parts are so old that the only replacements available are 30 years old and may not function at all)
For example, I've replaced two socketed SRAM chips with a single modern SRAM on a daughter board with pin headers aligned so that the whole circuit plugs into the two DIP sockets on the original board.
My question is, what is the actual name for this type of a board? Daughter board? Mezzanine board? I'm trying to figure out how to describe it in the tech notes.