Zen is about two things: emptiness of phenomena and emptiness of concepts/words.
The emptiness of phenomena is perceived through inwardly directed attention. This can be any type of self-inquiry, such as looking for the I-thought, feeling for the I-Am sensation, watching thoughts to find the gap between them, witnessing emotions, or immersing in the experience of them. Anything that gets you to experience your insides, including being better grounded in body sensations is appropriate/
The emptiness of words and concepts is more difficult to "get" because it means the total destruction of the world you thought you lived in. This kind of emptiness is different from the experience of emptiness, even though one can experience thoughts themselves as dissolving in space, or arising from emptiness as little cloud-like entities.
The emptiness of words and concepts is realized when you truly understand the difference between experience and phenomena compared with the world created by one's network of thoughts. The world and self created by words is absolutely different from the world directly experienced when thought stops. The no-mind world is experientially rich while the world created by thought is very narrow and fixed in comparison. The world experienced thoughtlessly is very fluid and constantly changing, while the world of thought is as fixed as the is the duration of the meaning of the words used in describing that world.
Strangely though, when you are thoughtless, empty, you are as fluid and flowing as the world so that nothing appears to move as your awareness is everywhere at once, containing and flowing along with experience and events. Then one is total spontineity, utterly flowing, uncontained yourself, and 100% responsive to whatever arises.
The Zen koan system was devised to systematically destroy the thinking mind of Zen students by helping them find the "sticking points" of "wrong" concepts, which when seen through, releases you from its fixedness. You relax and sigh, feeling a sense of relief because your world as you experience it, is less contracted than before, and you are more open to experience the real world than before. This process is progressive until you cannot be fooled by word-created problems.
Unfortunately the koan system grew out of an ancient Chinese culture, and thus irrelevant to the modern West. Seung Sahn's remake for the West is really too simplistic and truncated to provide the freedom ancient Zen masters enjoyed.
In spirituality there are many words you have to find as empty of meaning, empty of any object being pointed to, and thus be free of spiritual philosophy in order to experience yourself and the world directly.
These words have to been clearly seen as having no referent, nothing like these concepts exist in the world.
These words are just labels while experiences are alive. flowing, changing. This is the hardest thing to accomplish because the entire network of thought has the whole of society, education, science standing behind its reality and adding new concepts and words every day.
THE WORDS AND CONCEPTS THAT MUST BE REALIZED AS EMPTY, WITHOUT IN ANY WAY HELPING US TO LIVE IN OUR BODIES OR THE WORLD ARE:
non-dual; oneness, One; enlightenment; awakening; I; I-thought; I-sensation; ego; identity; Beingness; Now; God; self; Self; mind; emptiness; Void; truth; love; emotions; Chi; Kundalini; Shakti; Kali. Just to name a few.
The word 'emptiness' in no way conveys the experience of emptiness or the experience of an empty mind. Words are only maps, and everyone, depending on their backgrounds, reads those maps differently, and we can never know whether the words spoken by Mr. X, means to him what they mean to me. It is only when the network of thought is absent that we can feel that two people sharing nearly the same place in space and time, are experiencing the same thing.
Just as a hint, some comedians are dead on in making us aware of our hidden beliefs, preconceptions, ideals, and political correctness. Zen masters and other teachers also bring out and destroy our preconceptions about Zen, spirituality, life and love. Each day they eat away at our network of beliefs, habits, and inflexibility.