Slang for Viagra, Cialis or any other Erectile Dysfunction Meds. It is a combination of the word Viagra, Which is the most well know ED pill, and Niagara as in the popular water falls, because of the copious amounts of Jizz one produces while taking the Viagra.
-I took a couple of "Niagras" last night before banging the old lady, shot so much spooge I thought I'd need an I.V. afterwards.
-Don't take any of those "Niagras" tonight, my snatch is still sore from last Tuesday!