An erg is a unit of measurement or energy or work that is the same as 10-7 joules. It formed part of the centimeter gram second (cgs system of measurement that is no longer followed.
An erg is round about the amount of work done (or energy consumed) by one common house fly performing one "push up," the leg-bending dip that brings its mouth to the surface on which it stands and back up. 
References[change | change source]
- Filippenko, Alex, Understanding the Universe (of The Great Courses, on DVD), Lecture 44, time 24:30, The Teaching Company, Chantilly, VA, USA, 2007