Credit for a good deed, as in John earned a lot of brownie points for doing his boss's report for him. The term originated with the points earned for various achievements by the youngest group of the Girl Scouts, called Brownies. In the mid-1900s it was transferred to general use.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.