Kumite, also known as sparring, is ideally a realistic, highly spirited practice of sparring under the conditions most similar to actual combat. The only concepts missing are hostility and dangerous aggression.
The most significant concept of kumite is that of form. Any proper technique cannot be well executed without form. Almost anyone can execute a kick or a punch with total disregard to form, but the person who executes a technique with good form is well trained in this phase of karate. Good form in kumite comes in the manner of proper stance, good balance, and good posture. There is an aesthetic connotation in viewing a skilled contestant with good speed and good form.
More than anything else, kumite is really a test of wills. It allows the student to develop and improve elements such as (but not limited to) control, distance, form, focus, eye intensity, awareness, reflexes, coordination, and timing. It is an important tool in teaching the student how to apply the basic techniques, stances, and hip motions in a dynamic (rather than static) situation. 