(The wheel of Time, or the wheel of the Law) is the Teaching ascribed to the various Lords of Shambala. Traces of this Teaching can be found in almost all the philosophical systems and teachings of India. At the present time, it is perhaps more known in Tibet. But in reality, this Teaching is the Great Revelation brought to humanity at the dawn of its conscious evolution in the third race of the fourth cycle of Earth by the Lords of Fire, Sons of Reason, who were and are the Lords of Shambhala. (LHR I, p 401)
I approve of the Kalachakra, now being compiled. This fiery Teaching is covered with dust, but it should be proclaimed. Not reason but wisdom gave this Teaching. It should not be left in the hands of ignorant exponents. Many domains of knowledge are united in the Kalachakra; only the unprejudiced mind can find its way among these stratifications of all worlds. (FW I, 212)
Ah, now we once again approach our great Kalachakra: Who can exist without food? Who can exist without sleep? Who is immune against heat and cold? Who can heal wounds? Verily, only he who studies the Kalachakra.
The great Azaras who know the Teachings of India, know the origin of Kalachakra. They know vast things which, when they will be revealed to help humanity, will completely regenerate life! Many of the Teachings of Kalachakra are unknowingly used both in East and West, and even in such unconscious utilization, much that is wonderful results. It is therefore comprehensible how incomparably great would be the possibilities made manifest by a conscious achievement, and how wisely could be used the great eternal energy, this fine imponderable matter which is scattered everywhere and which is within our use at any moment. This Teaching of Kalachakra, this utilization of the primary energy, has been called the Teaching of Fire. The Hindu people know the great Agni - ancient teaching though it be, it shall be the new teaching for the New Era. We must think of the future; and in the Teaching of Kalachakra we know there lies all the material which may be applied for the greatest use. Now there are so many teachers - so different and so hostile to each other. And yet so many of them speak of the one thing and this very thing is expressed in the Kalachakra. ...
What is revealed in the Kalachakra? Are there any forbiddances? No, the lofty teaching sets forth only the constructive. So it is. The same high forces are proposed for humanity. And it is revealed most scientifically how the natural forces of the elements can be used by humanity. When you are told that the shortest way is through Shambhala, through Kalachakra, it means that achievement is not an unattainable ideal, but that it is something which may be attained through sincere and industrious aspiration here, upon this very earth and in this very incarnation. This is the Teaching of Shambhala. Verily, each one may attain it. Verily, each one may hear the pronounciation of the word, Kalagiya! ...
The harmony of exterior and interior can be attained only through the study of Kalachakra. Probably you have seen the signs of Kalachakra on the rocks, in quite deserted places.
Some unknown hand has set a design upon the stones or has chiseled the letters of the Kalachakra upon the rocks. Verily, verily, only through Shambhala, only through the Teaching of the Kalachakra can you attain the perfection of the shortest path. (S, pp 28-31)

This definition is in context to Classic Yoga. See more contextual defintions for Kalachakra.