Theory of relativity is a combination of two different theories orsays two different combinations. First, one is Einstein's specialrelativity theory and second one is general relativity theory.Concepts included in theory of relativity consider space-time asa single unified entity. According to concepts of theory ofrelativity, following are the elements of unified entity ofspace-time:Space and time (of course)Relativity of simultaneityKinematicDilation gravitational timeLength contractionTerm of relative theory was firstly used by Max Planck in1906. The whole theory of relativity is based on this term. MaxPlanck described how the principles of relativity theory could beapplied on practical events and various theories. Later on, inthe same discussion term Theory of relativity was used byAlfred Bucherer.Relativity theory is considered a unified representative ofmultiple physical theories. Concepts from more than onephysical theory are explained and broadly discussed in thistheory, which makes this theory real broad and deep. During20th century concepts and ideas of theory of relativity hastransformed many theoretical concepts of physics andastronomy. In the most basic version of theory of relativity,200-year old theory of mechanics was used as a base forfurther studies and descriptions. Isaac Newton is said to be thefounder of theory of mechanics, not the whole theory but hedeveloped and explained many concepts that are contained intheory of mechanics. The whole concept of gravity wasintroduced by him. In physics, theory of relativity contributed alot to develop or improve the concept of elementary particles.Concepts of relativity theory were used to understandinteraction of elementary particles more deeply. Theory ofrelativity also helped the world to move in the right direction toreach enhanced nuclear era. Not only in physics, have theoryof relativity also contributed in fields of cosmology andastrophysics. Thanks to the application in theory of relativity,astronomical phenomena were predicted and eventually provedreal too. These phenomena are consisting of following:Neutron starsBlack holesGravitational wavesAs described, Theory of relativity not only helps researches inphysics, but also in cosmology and astrophysics. This broadtheory became concern for cosmology since the basic conceptsas black holes are explained by theory of relativity. Manyconcepts that are a part of astrophysics use many conceptsand ideas of theory of relativity as a base for furtherresearches and explanation.