Basically it's a marketing term that may or may not have any real meaning. Anyone can stick "reference" on their product as there are no rules, regulations or criteria (that I'm aware of) for its use or meaning.
However, I believe most audiophiles would agree that true "reference" products have existed in the past and currently exist. But I think what was once a reference product, say in 1965 or 1980 is probably not one today.