The matra is the "beat" in Indian music. Along with the vibhag (measure) and the avartan (cycle), it is one of the three levels of structure for Indian rhythm (tal).

The unit of measuring tal is matra. The matra is determined in length by the pace of the overall rhythm. Each tal has a number of matras, as for example dadra has six matras. The number of matras does not change in vilambit, madhya or drut laya. Only the tempo or the time-sequence becomes slower in vilambit, average in madhya and faster in drut laya. A number of matras makes a tal, while the tempo determines the types of laya.
The smallest units the akshara (letter) and its several types are as follows:

Anudruta = 1 akshara = 1/4 matra
Druta = 2 akshara = 1/2 matra
Laghu = 4 akshara = 1 matra
Guru = 8 akshara = 2 matra
Pluta = 12 akshara = 3 matra
Kakpad = 16 akshara = 4 matra

The beats may have a different significance depending on where they come in the cycle. Beats that occur at the beginning of any measure (vibhag) are always more significant then the beats which occur midway in a measure. The first beat of the cycle (avartan) is the most important beat of all. It is called sam.

Indian music does not flow in metronome time; therefore the value of the beats may be stretched or contracted depending on numerous factors. This is easily demonstrated, but surprisingly enough is not acknowledged in traditional theory. One must understand the music thoroughly to know when such liberties are appropriate.

by David Courtney, Ph.D