Tapas is getting rid of all that is not you!
A small story:
Once a man went to visit a famous sculptor.
He saw the sculptor sitting silently in front of a big marble block,
smiling admiringly at it.
When he saw the visitor, he turned to him and said, 'Isn't she beautiful?'
'Who?' asked the bewildered visitor.
'This woman hiding in the marble block!' said the sculptor. 'Where? I don't see any woman!' said the visitor. 'You will, as soon as I finish removing all the unnecessary stuff around her!' smiled the sculptor.
On the spiritual path, this process is called tapas. Tapas is the intense, joyful effort that transforms you from what you are to what you can be. Of course, the sculptor was working on the marble, but the material on which you will be working is – Yourself.
Tapas is only for the very courageous, because it is at the same time the process of death and the process of birth. Tapas is death for your ego, because it involves shedding all the false ideas, and false concepts that you are carrying around, calling them as yourself!
The Sanskrit word 'tapas' literally means 'burning'. Tapas is the process of burning your ego with the fire of Truth. When you burn yourself with this Truth, letting IT penetrate into your being, it removes all that is false in you.
Tapas is not a spiritual practice to be added to you. It is the process of destroying all that is NOT you, so that whatever is really YOU may be revealed.