Never coxed or heard of the term?
Simply put, the coxswain is the (typically small) member of the boat who controls the speed and strength of the rowing; the cox is also responsible for steering the boat on a direct course. 
During practices a coxswain’s job is to execute drills and workouts in the boat, make sure the rowers remain focused, motivated and in time with each other. It’s also important to stick close to any other shells, to facilitate coaching.
During races a coxswain is the crew’s liaison with race officials on the course; he/she is responsible for steering the boat in the most direct path from start to finish, while executing a race strategy. Race strategies are usually planned ahead of time with the coach, but the coxswain must be prepared to make snap decisions and change the plan in the heat of the moment.
Like a horse and his jockey, it’s of utmost importance for the crew to trust their coxswain.

“The perpetual quest for improvement is a habit of success”