Taala is term used in Carnatic Music for a rhythmic pattern of any composition and everything that refers to rhythm. Its almost as same meaning as meter in Western music. It is a Sanskrit word that literary means 'clap'. 

When we talk about taala, it will resound a percussive instrument such as a Mridangam in Carnatic Music, 
Tabla in Hindustani and Drums in Western. It is a rhythmic cycle that has a beat with an ebb and flow of various types of intonations. Indian classical music has the most complex, all-embracing rules for the elaboration of possible patterns, though in practice a few taala's are very common while others are rare. 

The taala does not have a fixed tempo but can be played at different speeds. In Carnatic music, the singer will keep the speed or tempo by slapping the hand on the thigh and can fall into three categories; vilambitha kaalam, madhyama kaalam and duritha kaalam. 

One cycle of a taala is called an avartanam. A taala does not necessarily have evenly divided sections. The most common instrument for keeping rhythm in Carnatic music, is the mridangam. While the Vocalists mark the taala by tapping their laps with their palm, instrumentalists mark the taala by tapping their feet.

As heart beat is to life for a man, Taala lends life for whole of a concert. It is said "Sruthi Mata Laya Pitha" 
which means, the tone emanated from the Tambura is Mother to the music and the Tala is like father. 

Carnatic music uses a comprehensive system for the taala's, called the suladi sapta taala system. 
According to this system, there are seven families of taala's, each of which has five members, one each of five types or varieties (jati or chapu), thus allowing thirty-five possible taala's.

In Carnatic music each pulse count is called an aksharam. The interval between each aksharam must be equal, though capable of division into faster matras. The tala is defined by the number and arrangement of aksharam's inside an avartanam. There are three sub-patterns of beats into which all taala's are divided; 
dhrutam, anudhrutam and laghu.

A dhrutam means 2 beats (a tap and turn of the hand) and the sign is 'O'.

An anudhrutam means a single beat (a tap), and the sign is 'U'.

A laghu means a variable number of beats (a tap and count with fingers), 3, 4, 5, 7 or 9, depending upon the type of the taala and the sign is '1'. The number of matras in an aksharam is called the nadai or gati. This number can be 3, 4, 5, 7 or 9, and these types are respectively called Tisram, Chatusram, Khandam, Misram and Sankeernam. The default nadai 
is Chatusram.

Laghus that falls in each category is illustrated below (also called the five 'Jati's of taala):

Jati Laghu counts
Tisram 3
Chatusram 4
Khandam 5
Misram 7
Sankeernam 9

Taala description of an avartanam follows the seven families of the taala with respect to the laghu count of a particular jati. The seven families are:

Taala Avartanam Description Laghu counts Total Aksharam
Druvam IOII 4 14
Matyam IOI 4 10
Rupakam OI 4 6
Jhampai IUO 7 10
Triputai IOO 3 7
Atta IIOO 5 14
Eka I 4 4

For instance one avartanam of Misra-jati Triputa taala has a 7-beat laghu, 2 x 2-beat dhrutam, thus having an avartanam of 11 aksharam's.

With all possible combinations of taala types and laghu lengths, there are 5 x 7 = 35 taala's having lengths 
ranging from 3 (Tisra-jati Eka) to 29 (sankeerna-jati Dhruva) aksharam's.

Tisra-gati Khanda-jaati Rupaka taala has 7 aksharam, each of which is 3 matras long; each avartanam of the 
tala is 3 x 7 = 21 matras long. For Misra-gati Khanda-jati Rupaka tala, it would be 7 x 7 = 49 matra.

In practice, only a few taala's have compositions set to them. As in the table above, each variety of taala has a default family associated with it; the variety mentioned without qualification refers to the default. 
For instance, Jhampa tala is Misra-jati Jhampa tala.

The most common tala is Chatusra-nadai Chatusra-jaati Triputa tala, also called Adi tala (Adi meaning primordial in Sanskrit). From the above tables, this tala has eight aksharam's, each being 4 matras long. Many krtis and around half of the varnams are set to this tala. Other common talas include:

Chatusra-nadai Chatusra-jaati Rupaka tala (or simply Rupaka taala). A large body of krtis is set to this tala.

Khanda Chapu (a 10-count) and Misra Chapu (a 14-count), both of which do not fit very well into the suladi sapta tala scheme. Many padams are set to Misra Chapu, while there are also krtis set to both the above taala's.

Chatusra-nadai Khanda-jati Ata tala (or simply Ata tala). Around half of the varnams are set to this tala.

Tisra-nadai Chatusra-jati Triputa tala (or simply Triputa tala). A few fast-paced kritis are set to this tala.

Sometimes, pallavis are sung as part of a Ragam Thanam Pallavi exposition in some of the rarer, more complicated taalas; such pallavis, if sung in a non-Chatusra-nadai tala, are called nadai pallavis.

Eduppu or Start point is another common term use in the taala system. Compositions do not always begin on the first beat of the taala: it may be offset by a certain number of matras or aksharas or combination of both to suit the words of the composition. The word 'Talli', used to describe this offset, is from Dravidian and literally means "shift". A composition may also start on one of the last few matras of the previous avartanam. This is called Ateeta Eduppu.