This article reveals the essence of the special theory of relativity. To date, there have been no scientific arguments against the proofs presented at the 3rd Annual International Conference on Physics in 2015 in Athens, Greece. The "Introduction" presents the foundation of the real explanation of all "unexpected" and "inexplicable" results of the experiments related to the measurement of the speed of light in our time-spatial region "near the Earth’s surface". Subsequent factual analyses of the most famousexperiments related to the velocity of light behaviour prove that the speed of light differs in different directions from the local constant "speed of light in vacuum". The exception is only the experiments that use the "Michelson-type" interferometer. These interferometers use perfectly the same paths in two opposite directions for each light beam, which is why the difference between the speeds of light in the two opposite directionsof each light beam is completely compensated. The analysis of the article "On the Electrodynamics of Moving Bodies" shows exactly where and how the claim "the speed of light is the same for all inertial frames of reference" is applied. Einstein’s conclusion that "we cannot give anyabsolute meaning to the concept of simultaneous" is unfounded and absurd and is shown to be based solely on this erroneous claim. At the end of the article, the essence of the so-called "fundamental tests" of the special theory of relativity is presented too.