Napkin Engineering

The use of a napkin to illustrate, design, invent, or otherwise explain some kind of engineering topic, theory, process, or equipment.

Envelopes, hands, and other generally small pieces of paper can be substituted.

Aristotle- How was the napkin ring invented?

Plato- I drew it on the back of a napkin.

Aristotle- Oh, napkin engineering. Toss the fris!