Boiled down, a super Earth is an exoplanet that is between the Earth (and actually smaller than than Earth, I’m guessin’) but smaller than the Uranian-Neptunian “ice giants”. Oh, and it has to wear the cape.
Even "substantially lower" (mass) is a bit of a loose constraint, I guess: 12.9x Earth vs. 14.5x does not seem a whole lot lower than Uranus, tho' we're getting there with Neptune (17x), I suppose. I propose 10x to 14x as "Super Duper Earths". Heheh. *Looking into this, I was reminded how cold Uranus atmosphere is, as low as -225 deg. C and 560 mph winds. Yikes!