Ektal is a very popular tal. It is is common in classical music such as the kheyal, and semiclassical forms such as Rabindra Sangeet.
The structure of ektal is simple. It is 12 matras divided into of six vibhags of two matras each. Its clapping arrangement is clap, wave, clap, wave, clap, clap.
It is most associated with the kheyal style of singing. A particular movement known as bada kheyal or vilambit kheyal is performed almost exclusively in very slow ektal. However, ektal is also performed in fast kheyal as well.
The name "ektal" literally means "one-clap". How the name came is a mystery since it has four claps
clap, 2, wave, 2, clap, 2, wave, 2, clap, 2, clap, 2
12

Note - This excerpt has been taken from "Learning the Tabla"
(general discussion of theka)For more information check out "Learning the Tabla"