Motivation or willingness to do something — the drive or enthusiasm; commonly used in expressions like 'have/no motivation'.
最近仕事のやる気が出なくて困っている。
Lately I haven't felt motivated for work and it's troubling me.
上司の励ましで部下のやる気が戻った。
The boss's encouragement restored the subordinate's motivation.
やる気があれば、難しいことにも挑戦できる。
With motivation, you can take on difficult challenges.