The opposite of dukkha. Pleasure, not suffering. In meditation, one realizes that pleasure is just the absence of suffering and it, like suffering, is impermanent, annica.

So one loses one's attachment to pleasure. It merely changes into dukkha and dukkha changes into sukkha, and so it goes.

Buddhist practice takes the practitioner off the wheel of dukkha, sukkha, dukkha, sukkha, dukkha...