The teaching of Chan is ancient and mysterious, it has a special way to teach people to open their minds and understand their lives, and for ages to come, it will give people concepts and experiences that are hard to grasp and are out of the ordinary. So in ancient times from the noble Emperor Qin to ordinary commoners everybody liked Chan wisdom very much and even currently in modern society Chan teachings are increasingly fashionable all over the world. However according to most people and their understanding of Chan, they think that only if they sit cross-legged is considered Chan meditation practice. This is actually a misinterpretation of the principles of Chan, sitting meditation is only one form of Chan's outward manifestation, just like Wushu Chan (Zen martial arts) promoted by the Shaolin Temple, which is another form of Chan's outward manifestation.
So what is Chan after all? How is it possible for it to have such a wide range of following and application? This is a question that a lot of people who are interested in studying Chan are very concerned with. Below I will discuss in simple terms what Chan is, starting from the meaning of its name all the way to its essence. Explaining Chan from its name, it's the transliteration of the Sanskrit word "Dhyana" into Chinese "Channa", later abbreviated as Chan. Venerable Master Kumarajiva of the Qin Dynasty translated it into "the cultivation of contemplation", that is cultivation using the activity of thoughts whereas the Tang Dynasty's Venerable Master Xuanzang translated it as still or quiet contemplation, which is the cultivation of single-mindedly focusing on one object and properly examining thoughts.
If we use still contemplation to explain the meaning of the name Chan, the word "still" in still contemplation has the meaning of stopping or ceasing, also carries the meaning of being set (fixed) or stable, and contemplation also carries the meaning of observing - observation that gives rise to wisdom. In the process of Chan practice, we must maintain balance between stability and wisdom, if we incline more towards stability that will result in dullness, and if the balance tips over in favor of wisdom that will result in delutedness. Stability and wisdom, these two aspects complement and complete each other, they cannot be separated. So if we explain the meaning of Chan from a naming perspective, Chan can be called "still contemplation", "stopping and observing", "stability and wisdom" and so on. However these names don't convey the real intention of Chan, they only explain the meaning of the name Chan. Chan has a lot of different forms and methods, but it has only one fundamental principle. Regardless of what style or method you are using, most importantly you should be clear on the essence of Chan. Explaining Chan from the aspect of its essence, it's the process of first getting to know ourselves, then getting a hold of ourselves, that is to develop and control ourselves according to our views/vision/goals, and finally purifying ourselves and perfecting ourselves. In other words Chan is the process of constantly working towards liberating ourselves. Chan practitioners must see this point clearly. Once we understand that we just have to find a suitable method of training and work towards validating the practice of Chan for ourselves: to experience for ourselves how to understand our own mind states, control our own mental activities and concentrate our mind and intention to examine what we are doing (our internal processes). Therefore we do not not necessarily have to practice sitting meditation to implement this process, but we have to strive to accomplish this task, no matter what kind of state we are in. This process can always be implemented. Just like it's said in Chan Master Yong Jia's teachings: "Walking is Chan, sitting is also Chan; speech and silence, movement and stillness, all is at peace, quiet the mind." This is exactly where Chan's fundamental meaning lies. What has been said above is just an attempt to use language in order to introduce Chan in a simple manner. However, true Chan cannot be conveyed by any words or language, because Chan is a subjective experience of our innermost being, only if we have experienced it for ourselves will we be able to understand it. Just like as it's often told (in Chinese circles I guess): "Chan is a realm of its own, a realm of our consciousness." This realm could be likened to a person drinking water, only he will know its temperature. In other words we have to experience it for ourselves in order to really know what Chan is.