[Pali “out-of-alignment”] Variously translated as suffering, pain, sorrow, discontent, imperfection, sin, evil. In Buddhist doctrine, dukkha is one of the three characteristics of existence—along with anicca, impermanence, or transience, and anatta, non-separateness (having no separate soul or ego; no exclusive possession of the immortal spirit).
The Four Noble Truths, which Gautama Buddha taught his disciples, state that 1) life is dukkha, 2) the cause of dukkha is desire, 3) freedom from dukkha is in the attainment of Nirvana, 4) the way to this liberation is through the Eightfold Path: Right Understanding, Right Thought, Right Speech, Right Action, Right Livelihood, Right Effort, Right Mindfulness, and Right Concentration (or Right Absorption).
Pearls of Wisdom, vol. 29, no. 77.