Heaven - Represents Divine and Cosmic Order. The law that binds everything together. The ultimate truth adhered by mortals and cultivators alike. It's also associated with Yang.
Earth - Represents the physical world that beings live in. It symbolizes birth, growth and stability. It's also associated with Yin.
World (Tianxia) - Everything under the Heaven. It can be a bit confusing, but world can refer to both Earth, or the entire universe at large. Don't worry, the context will help mitigate any misunderstandings.
Cultivation Art - A complex truth of the Heavens revealed to the beings. It can be created by imitating nature or by gaining enlightenment. A cultivators follows the teachings of these arts to build foundations for their cultivation.
Martial Art - A form of technique that utilizes physical form and vital essence. Most work toward enhancing their users, while some hold enigmatic effects. Usually requires stimulation or burning of Vitality.
Utility Art - A technique that utilizes Qi for a variety of activities. These can be both combat oriented or for general purpose like baking a bread. [Note that Alchemy, Blacksmith, and Inscription profession applicable methods don't come under this category.]
Spirit Art - Methods that utilize Soul Force to perform a set task like igniting fire or manifesting water.
Qi - A form of energy capable of stimulating the force of evolution inside a being. It's the vital life force that permeates everything in the universe.
Meridians - Channels or pathways inside a being that circulate Qi, from body to dantian and dantian to body. Over the course, due to long term exposure these Meridians undergo a transformation that brings their existence closer to energy form than material form. Exact mechanics will expounded on in the story.
Dantian - The energy center of being that stores all their Qi. It's a physical organ, but given enough breakthroughs, it also holds the capability for transformation into something that's more energy than matter. It's connected to all the Meridians inside a body. Destruction of this organ will result in one becoming a cripple.