Definition - What does Tapas mean?
Tapas are spiritual practices that often involve a high degree of self-discipline, solitude and periods of deep meditation. The word comes from the Sanskrit root word tap, which means "the heat needed for birth." This relates the word to the concept of spiritual rebirth and the inner fire needed to achieve it.
Disciplined, spiritual yoga practice can be one type of tapas. Someone who undertakes tapas is known as a tapasvin.
Yogapedia explains Tapas
Ancient Indian texts state that achieving knowledge of Atman (the true Self) is the goal of tapas. It is also sometimes referred to as a spiritual rebirth or transformation.
Yoga practice is linked to tapas in that both require meditation and periods of calm reflection. Indeed, it is said that yoga is a type of tapas, because of the discipline and effort necessary to practice yoga in a meaningful way. The self-contemplation that happens in yoga practice can help lead one to a better understanding of their atman, which is the goal of any tapas.