Yoga Sutra 2.32 Niyamas: Enthusiasm - tapas
Tapas is an invitation to participate in every moment with passion and motivation.
Tapas is the fire that helps us overcome our tendency to predict and to assume that we already know what will happen. Tapas is also the heat resulting from the friction or going against the grain of our habits. Concentration, another meaning of tapas, is necessary to notice if your habits are useful or harmful.