In Buddhist meditation, Sukkha is a type of emotion and one of the factors of Jhana. It consists in a quiet happiness, while Piti mentions a deep joy, rapture.

Piti is a deep joy, maybe with smiling, laughter, etc.

Sukkha is a quiet joy, where you contemplate the joy, and you don't respond to it by laughing, but are merely content in that joy.

All the factors of the First Jhana overlap to a degree.