When I take out the dog in the morning, I first look outside to see the temperature. A few days ago it was 56 degrees F. When I got outside it seemed to be cold to me; however, in the winter that same temperature would be considered warm if not down right hot. Proving that temperature to me at least is relative.
Time seems relative also. When we are busy "time flies"; but waiting for the time to leave work when your work is done but the clock hasn't realized that it should be later "time drags". In the Navy, the last few days of any deployment seem to last forever. Waiting to get to sleep seems to last forever but morning quite often comes much too soon.
I always found that car trips to a place seem to take longer than the reverse. 50 miles to work each day seem to take a long time but 50 miles to visit a friend or relative are much easier to traverse.
Special relativity is a theory of the structure of spacetime. It was introduced in Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies". Special relativity is based on two postulates which are contradictory in classical mechanics:
The laws of physics are the same for all observers in uniform motion relative to one another (Galileo's principle of relativity),
The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.
The resultant theory has many surprising consequences. Some of these are:
Relativity of simultaneity: Two events, simultaneous for some observer, may not be simultaneous for another observer if the observers are in relative motion.
Time dilation: Moving clocks are measured to tick more slowly than an observer's "stationary" clock.
Length contraction: Objects are measured to be shortened in the direction that they are moving with respect to the observer.
Mass-energy equivalence: E = mc2, energy and mass are equivalent and transmutable.
from : WikiPedia Special Relativity