A more academic English translation of the Spanish word "cojones", that originally stood for testicles, two spheric glands part of the reproductive system of males, also commonly known as balls.
To have testicular fortitude is to show strength, courage and sagacity in challenging situations. The story of how strength and courage is related to two nuts encased in shriveled skin hanging from between a man’s legs is a fascinating story that i don't have the time to go into right now.