Prowess means exceptional skill or ability. Your sailing prowess might save your life in a storm, while someone with less experience might make mistakes.
An earlier meaning of this word is exceptional bravery in battle, or a specific act of bravery. Prowess is a Middle English word borrowed from the Old French proesse, "courage, brave deed," from prud, "good, capable, brave." The related English word proud originally had the now obsolete meaning of "brave."