Hey man! Brush stroke economy is a fairly advanced outcome of mastering formal realism in rendering/painting. It means representing anything with much fewer paint brush strokes, using only a few well placed marks instead of the hundreds of overlapping strokes a novice would use to represent (and overwork) something.
A traditional master of brush stroke economy is John Sargent, who uses a mesmerizingly small amount of brush strokes to achieve a realistic look. In the digital world, there is Craig Mullins, you should also look him up!
When I submitted my asset sheets to Marc Brunet for review, he said I was fairly advanced and recommended I start looking into brush stroke economy to become more efficient. It's a compliment, but also a daunting challenge. Gonna start painting with that in mind!