Void means "emptyness". In your example of void main() it means that the functions main() does not return a value. I feel obliged tell you that void main() should be avoided (no pun intended) at all costs, use int main() instead. int main() makes sure your program can return a value of type int to the OS on close.
What is the use of void?
Void functions are created and used just like value-returning functions except they do not return a value after the function executes. In lieu of a data type, void functions use the keyword "void." A void function performs a task, and then control returns back to the caller--but, it does not return a value.
What is the purpose of the void?
When used as a function return type: the void keyword specifies that the function does not return a value. When used for a function's parameter list: void specifies that the function takes no parameters.