Why is there oil on my floorboard?

Taste it.
Seriously, if it's coolant it'll be sweet tasting and oil won't be.
just don't swallow any of it. :-)

People think I'm kidding when I tell them that but it sure defines it quick.

Coolant= sweet
Oil= tastes like oil
Trans fluid= like oil with an odd difference.
Brake fluid= bitter

It's probably coolant though just because of the location.