Adaptive ability - adapting to an action or sequence in anticipation to changing conditions.
Balance - static and dynamic equilibrium.
Combinatory ability - coordinating body parts or a combination of body parts to created a coordinated action or movement.
Differentiation - accurate, economical adjustment of body movements and mechanics.
Orientation - spatial and temporal control of body movements.
Reactiveness - quick, well-directed response to stimuli.
Rhythm - observation and implementation of dynamic motion pattern, timing and variation.
To generalize, agility deals with an athlete or individual's ability to control acceleration, maximum-velocity as well as multidirectional skills.
Skill classification can be broken down into 3 categories; General vs. Special Skills, Closed vs. Open Skills, and Continuous vs. Discrete vs. Serial Skills.
General vs. Special Skills
General agility tasks target the development of one or more basic coordinative skills. Special tasks would then unify or combine general skills or tasks into more specific movements. Special skills are more related to specific practice specificity for an action or sport skill.
Closed vs. Open Skills
Closed skills are those in which there are predetermined and unchangeable variables. In these types of training modes, the athlete or individual has predictable or stable environments. Examples of a closed agility skill would be a timed T-test or agility drill. An open skill would be one that has unpredictable or unstable factors involved. Examples would be real-time sport games or practices such as a football running back dodging a defender or a baseball player fielding a ground ball.
Continuous vs. Discrete vs. Serial Skills
Continuous tasks have no definite beginning or end. Discrete is the opposite of continuous as they have a very defined beginning and end (100m sprint). Then, serial tasks are a number of discrete tasks completed in sequence.
Change in Velocity
Many sports or athletic activities require a specific change in velocity. Sure, there are many variations dependent on the type of sport or activity, the number of players in the field of play and even differences in playing surface but all changes in velocity have a few things in common.
I find velocity changes to be one of the most important and crucial tasks to perform in order to be considered "agile". Changes in velocity typically involve an initial velocity, a deceleration, and change in direction, and then another increase in velocity (acceleration).