Hand clapping is called Taali. "Clap", an accent of stress, marked by clapping, which delineates the structure of a Taal (Rhythm).
Khali (Empty)
It means a gap of some Matras (beats) which indicate by palm putting on left side (if you are clapping with left hand) and reproduce no Bol (note) or show empty
Taal (Rhythm)
Taalis divided into several sections because this makes it easier to understand and recognize (the x-o indicates where one section ends and a new one begins).
Theka
Theka is composition of bols (notes) with Taali and Khali, grouped into several sections in different matras (beats). Fixed composition presents the basic structure of a Taal (rhythm).
Variation
Every theka can be played with a difference or with variation.