The term of relativity theory was firstly used by Max Planck in 1906. The whole theory of relativity is based on this term. Max Planck described how the principles of relativity theory could be applied to practical events and various theories.
Relativity theory is considered a unified representative of multiple physical theories. Concepts from more than one physical theory are explained and broadly discussed in this theory, which makes this theory both broad and deep. During the 20th century the concepts and ideas of the theory of relativity have transformed many theoretical concepts of physics and astronomy. In the most basic version of the theory of relativity, the 200-year old theory of mechanics was used as a base for further studies and descriptions. Isaac Newton is said to be the founder of theory of mechanics, not the whole theory but he developed and explained many concepts that are contained in theory of mechanics. The whole concept of gravity was introduced by him. In physics, the theory of relativity contributed to the development of the concept of elementary particles. Concepts of relativity theory were used to understand interaction of elementary particles more deeply.