Well, the term Ascension can Refer to many Different things Ranging from the Bible – to Ancient Drawings found in Caves, tombs, & Pyramids.
However to sum it up to the best of my Ability it goes like this;
Ascension is the process in which the soul and form become one vessel, thus ceasing the need for the form altogether, i.e., the form moves into the non-physical realms along with the soul. It is through the process of ascension that all souls along with their creation known as form eventually returns to the source or God/Goddess, So in other words It is when the Human race dies, and all of our Spirits/souls are Returned to the Source of our Creation (The Center of the universe) or “Heaven” in most cases.
It is Strongly Believed by some, and there is Even Drawings found in Ancient places of the Ascension, Although no one knows when Exactly this will Happen, there is talk about the year 2012 Hence all of the Mayhem over the Mayan Calender, Which dose not end it just starts a new Cycle.