We pulled up an antique carpet runner on our original 70+ year old hardwood floors. Yes, they need to be refinished but was trying not to do that this year. The stain looks like the pattern of a spilled drink, possibly from my son's ice tea or clear Gatorade. The crazy part is it is bright almost fluorescent yellow. I've tried hand sanitizer and hair spray (for the alcohol) which yellowed the towel we were rubbing with, but did not really remove any. Regular hardwood floor cleaners did nothing. Could it be an acidic drink reacting with the old varnish? The area is over 5 boards, about 4 feet long. Believe the wood is honey maple, from the wear I think it was finished about 20+ years ago. Thoughts? Please don't suggest vinegar.

Sometimes a latex backing on an area rug can have a chemical which keeps the backing pliable will bleed the chemical into the film finish. This will dissipate after a while if the rug is removed. It produces a yellow color and darkens the floor in that spot.
You can ask a janitorial company what they recommend for cleaning the spot. A janitorial supplier might have the right cleaner for you, too.