It means your tv or monitor is only mono (not stereo) if it has only the one audio jack.
You could just plug either the red or the white into it and have sound, but with the SNES being stereo, you'd only hear the left or the right channel audio, which could be weird depending on the scene in the game, but certainly playable.
Your best bet is to get an adapter that couples the red and white audio jacks out from the SNES and converts them into one output jack. You wouldn't get stereo, but you would hear both the left and right channels. Should be less than $5
Like this:
http://www.parts-express.com/Data/Default/Images/Catalog/Original/240-127_HR_0.jpg