What is a "reference" system?

It is the system you "refer" to when comparing it to others.

I still use a boombox in the garage. I have my desktop plugged into an old receiver and some small Yamaha 2 way speakers in the office.  I. have another system in the basement.  None of these I would call Reference.  My main setup is much higher quality and as such would be my reference when listening to any other systems.

It would seem to me that a reference system would be a system that was used, or similar to that used, in the mixdown of the track of the specific recording being played at the time.

For example, there can be no denying that LS3/5As are "reference" speakers regardless of size or price.

Everybody's system is "their" reference system. It's really that simple.

Fast freight said about all that needs to be said... "To me, it is the system with which I use to compare other or new things". Would that be fair comment?

+1 @fastfreight