Abduction - Moving a limb or any other part away from the midline of the body. Abduction is the opposite of adduction. (e.g the "up" phase of a jumping jack involves the abduction of the legs and the arms, or spreading of the fingers and toes).

Adduction - Moving a limb or any other part toward the midline of the body. Adduction is the opposite of abduction. (e.g the "down" phase of a jumping jack involves the adduction of the legs and the arms, or bringing fingers and toes together).

Compound (Compound Exercises) - Exercises involving motion in more than one joint and targeting more than one large muscle group. (e.g. the squat or the leg press, with joint motion at the hips, knees and ankles, targets the gluteus, hamstrings, quadriceps, ankle flexors, and calf muscles).

Cool Down - The time at the end of a workout allowing the body to return to near resting levels. Cool down includes an active aerobic cool down and a final cool down consisting of stretching exercises.

Extension (Extend) - Movement in a joint by bringing two parts into or toward a straight line, increasing the angle of the joint, such as straightening the elbow. Extension is the opposite of flexion.

Flexion (Flex) - Movement about a joint in which the bones on either side of the joint are brought closer together, decreasing the angle of the bones forming a joint. Flexion is the opposite of extension. (e.g. bending the elbow or a biceps curl).

Isolation - Exercises involving motion at one joint, targeting one specific muscle. In a properly performed bicep curl, the joint motion occurs only at the elbow and targets only the biceps muscle.

Lateral Rotation - Turning the axis of a joint away from the midline of the body. Opposite of internal or medial rotation, but synonymous with lateral rotation (e.g. turning the shoulder outward externally rotates the shoulder, or turning the toes outward externally rotates the lower leg).

Prone - Lying in the face down position. Prone is the opposite of supine.

Repetition (Rep) - The number of times a specific exercise is performed within a set. (e.g. 10 push-ups without rest).

Rotator Cuff - The "cuff" formed by four muscles and their tendons, acting to stabilize and reinforce the humeral head in the shoulder joint during movement.

Sets - A number of repetitions performed without any rest. (e.g. one set of ten repetitions or 1 x 10).

Speed of Movement - The speed at which repetitions are performed.

Stretching - The act of elongating (making long) muscle and connective tissues to improve range of motion around a joint.

Supine - Lying in a face up position. Supine is the opposite of prone.

Source:
The Total Trainer, Army Physical Fitness Research Institute, The U.S. Army War College Barracks, Pennsylvania.