Essence-function, or 體用 (tǐyòng) in Chinese, refers to two important aspects of something. Let's say you have a toy car. The car's essence is what it's made of: metal, plastic, and other parts. Its function is what the car can do: roll on wheels, accelerate, and move forward and backward.
Essence and function are important because they work together to give something its purpose. For example, the purpose of the toy car is to provide entertainment and enjoyment to the person playing with it. The essence and function work together to achieve that purpose.
In Chinese culture, essence-function is often used to describe the relationship between things like art, literature, or martial arts. The essence is the fundamental principles, theories, and techniques of the artform. The function is the way those principles and techniques are applied in practice to create something beautiful or effective.
So when someone talks about the essence-function of an art, they're talking about the way theory and practice come together to create something meaningful and valuable. It's like how the wheels and motor of the toy car work together to create a fun and engaging experience for the person playing with it.