Titans was a general name given to the primordial entities on earth. They represent fundamental elements and the nature itself. The term titan was firstly used by the greeks, representing them as old gods who reigned before olympic gods.
It is believed that Titans appeared as superior entities who linked the metaphysic and physic dimensions. Each one was closer to a particular physical or methaphysical phenomena and thus they were named by this relation. The number of primordial entities is not clear and there are no deep knowledge about it. It is commonly accepted that they come to life few moments after universe origin.
Greeks were the first civ to use the term Titan. Theese older gods were related to nature: Chronos, Uranus, Gea etc. who are related with time, sky and earth are examples of that condition. Most of the greek titans are accepted as truly titans while others are considered latter deities.
As well as greeks, there were primordial entities in norse mythology. Despite they weren't call Titans, Ymir is consideres as that; even primordial worlds of fire and ice are believed to be primordial entities.
Existence of titans is not clearly recorded, ancient manuscripts and different oral and written tradition stories give most of the known information. However, it is clear that they are deities and keep all their qualities, they're inmortal and have a great power outstanding even against angels and archangels.
Some wise men describe them as "might, ethernal but counscienceless being". it has sense since, as primordial entities, they represent the primitve and irrational forces of nature.