I personally believe every topic should be explainable in one sentence or less.  For example,

Mechanical Engineering - The study and application of position, velocity, and acceleration to determine the forces and moments acting on an object.

Christianity - The religion that emphasizes personal salvation through the sacrifice of Jesus Christ as a means of accessing and drawing closer to the God of heaven and earth.

Rocket Science - The study of objects in flight assisted by an active propelling force.

See?  Simple.  Whenever I need to ask a long talker to explain something, I usually specify to do it in one sentence or less.  If they can't, they're not trying hard enough.  If they don't, I don't listen. #language