By inference - one possible definition extracted from "Follow Your Neighbor" is "the Person next to you before you started to a particular move". This would be a good enough definition for my needs. But I'm curious to find out if there is an agreed definition.
This notion has definitely fallen out of use today. In my opinion, all challenge dancers/callers, and most advanced dancers/callers are taught that from a Wave, the ends and adjacent dancers are Partners (in the formation). This is necessary for calls such as Partner Tag.
These URLs (old definitions) mention "Neighbors":
