Willpower is the ability to overcome urges to do or not some activity– to overcome temptation. Typically there is a sense of coercing oneself to do things despite inner resistance.
Willpower is of interest those who wish to increase their productivity or otherwise do more thing that they wish to be done. The question then is "how does one increase willpower?"
There is an argument that the use of willpower is undesirable. The use of willpower my constitute a form of inner violence which is in tension with inner alignment of one's parts– a better path to productivity and wellbeing.
Related: Akrasia