Center of mass (CoM): is the point around which we balance our body mass, or the point where gravity appears to act on the body (also known as the center of gravity). If three planes divide the body in equal parts of mass between front and back, left and right, and top and bottom, the CoM will be the point where all three planes intersect.
Center of pressure (CoP): is a measure of the distribution of pressure between the two feet and between the front and back of the feet. Since pressure is a measure of force, the CoP can also be defined as the point on the surface through which the sum of the GRF acts.
Ground reaction force (GRF): refers to the force exerted on the golfer by the ground in response to the force exerted by the golfer on the ground. It is defined as mass multiplied by acceleration, and is measured in newton (N). The laws of motion dictate that for every action there is an equal and opposite reaction. The GRF is always present as long as there is physical contact with the ground and works in all directions in which the golfer is exerting force on the ground.
Horizontal force: refers to the horizontal component of the ground reaction force (see Ground reaction force). This is typically separated in two directions: forces working sideways (mediolateral forces) and forces working forward and backward (anteroposterior forces). The golfer can increase or decrease the horizontal force through movement, by accelerating the body in various directions. Note that horizontal force increases with increased vertical force (see Vertical force).
Mass: is a measure of how "heavy" an object is, and is measured in kilograms (kg) or pounds (lbs). For example, you could say that your body mass is 85 kg (or 187 lbs).
Pressure: is a measure of the force acting over an area (in other words, force divided by the area over which the force acts).
Pressure shift: refers to the changes in pressure distribution, reflected in movement of the CoP. Note that we have chosen to move away from the use of "weight shift" to describe the movement of the CoP since it is an inaccurate description (see Weight shift).
Rate of torque development: is a measure of how fast the golfer is able to increase torque, and is measured in newton meters per second (Nm/s). Graphically it can be seen as the steepness of the torque curve toward maximum torque. The rate of torque development is a measure of the golfer's explosiveness.
Torque: is a measure of rotational force, and is measured in newton meters (Nm).
Vertical force: refers to the vertical component of the ground reaction force (see Ground reaction force). The vertical force experienced by the golfer is directly affected by the acceleration of gravity, since it works vertically. In addition, the golfer can increase or decrease the vertical force through movement, by accelerating the body away from or toward the ground.
Weight: is the force of mass caused by the acceleration of gravity, and is measured in newton (N). For example, if your body mass is 85 kg (or 187 lbs; note that force is always calculated from mass in kg), your weight is 834 N (85 kg * 9.81 m/s2).
Weight shift (also known as weight transfer): refers to the movement of body mass, or more specifically the CoM, since weight by definition is a measure of mass (see Weight). Note that weight shift primarily is a coaching term rather than a biomechanical term.