Definition - What does Tapa mean?
Tapa is a Sanskrit word referring to one of the five niyamas that reveal to those on a spiritual path how they should continue their journey.
Tapa is commonly translated as “endurance.” It can be thought of as a way of carrying on with good spirits when "the going gets tough."
Yogapedia explains Tapa
The idea of tapa encourages the yogi to not desist from their useful habits due to physical or mental difficulties encountered along the way. One may feel that the discomfort they experience puts them off of the idea of continuing; however, by showing endurance, the yogi can continue to make progress.
There are three different types of tapa. These are known as sattva, tamas and rajas. They each denote a different approach to the idea of endurance through difficult moments or discomfort.