In golf terms, an eagle is defined as a player finishing two strokes under par for a single hole. In other words, if a player sinks the ball in three strokes on a hole indicated as par 5, that is deemed an eagle.
Scoring an eagle takes a tremendous amount of skill (or luck) and does not happen often in the sport. Eagles most commonly occur on par 5's, but are also possible on holes designated as par 4 or 3. On occasion, an eagle will happen simultaneously with a hole-in-one, when a player scores a hole-in-one on a par 3, it is also deemed an eagle. The term was derived as an extension of the golf term birdie, which means shooting one stroke under par.