what's an oscilloscope?

I had a couple guys here installing a high tech propane house furnace. Renovations also going on. The house is chaos. I had my Tektronix 7854 and 7L5 in the living room on the cart. One guy asks what it is? I reply the first oscilloscope with a computer. What's an oscilloscope? he asks. It lets you see electricity I replied. He seemed happy with that. Age about 40. What's an oscilloscope?

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada