"Proficiency" in FAR Part 61 is used in two different senses, or connotations. The first relates proficiency to the annual proficiency check that's required for the pilot-in-command of an aircraft that must operate with two pilots. This check consists of the maneuvers and procedures required for a type rating or a practical test in such an aircraft (FAR 61.58d).
The second connotation is more revealing. It relates proficiency to the pilot who is working toward a pilot certificate (recreational, private, commercial, airline transport pilot, or flight instructor) or a pilot rating (multiengine or instrument). Here, the term "flight proficiency" is always followed by the term "areas of operation" (FAR 61.63(b)(3), 63(c)(2), 65(c), 98, 107, 127, 157, and 187). "Areas of operation" is a direct reference to the applicable PTS.
Each area of operation and its related tasks describe the knowledge and performance requirements for pilots who seek or who hold that certification or rating. Proficiency exists when pilots can perform the tasks as specified.
General aviation flight training improved dramatically when the FAA embraced the train-to-proficiency philosophy and developed the PTS. Pilots and instructors commonly think the PTS pertains to training only, but I'll let you in on a secret. The PTS is more important to you after training than during training, when you were under flight instructor guidance.
One of the most important components of proficiency is your mental posture - your awareness of the flight procedures, rules, and piloting skills that apply to the certificate and ratings you hold. If you use the PTS to maintain the correct mental posture, your proficiency level will rise and your proficiency training expenses will decrease.
Let's use the private pilot PTS normal crosswind approach and landing task as an example. It says:
Here's the trick. Turn off the TV, sit in your favorite chair, and review a specific PTS task. Now, close your eyes, imagine yourself in an airplane, and mentally fly the task. Using the example, you would "fly" normal and crosswind approaches and landings until you develop complete awareness of the task's procedures, rules, and piloting skills. When time permits, go to the airport and shoot some actual approaches and landings to reinforce your mental posture. Your performance and self-confidence will surprise you, and you'll discover that proficiency is more than a word.