Dukkha – Sanskrit term from Buddhism meaning “suffering,” but more precisely “dissatisfaction,” “anxiety,” or “unsatisfactoriness.” It can be the physical pain sickness, injury, death, or grief, but it can also be the result of trying to grasp and hold things that are always and permanently changing. This type of dissatisfaction can also be a result of trying to hold onto a vision of how things should be according to our own judgment. It is the core of the First Noble Truth of Buddhism.
Another example of unsatisfactoriness might be that feeling after you win a big race or the lottery. Not right after, but after maybe a few days or a few months. You might still feel unfulfilled. It’s that “now what” feeling after you get/accomplish something that you thought would make you happy.