Its a green sticky goo that you inject into your (deflated tyre) then inflate to the correct pressure. You then take your bike for a spin and evenly coat the inside. You can then bang a nail in to the tyre and pull it out and hey presto instant nano second seal with no loss of pressure. It is tested to 180mph and gives you the security of never getting a puncture and getting the full life out of the tyre.
Although I don't have it in my current bikes (I will have soon) I have used it in the past to repair a puncture and it is brilliant.
Its only a stupid question if you know the answer brother!