Ghazal is a verse form, and can be composed in any language. It consists of couplets called ‘Sher’, and follows the rules of ‘Bahr’, ‘Radif’, ‘Qaafiya’, ‘Matla’, and ‘Maqta’.
We will use following ghazal by poet Saeed ‘Rahi’, and sung by Pankaj Udhas, to understand these rules:
kya jaane kab kahaan se churaayi meri ghazal
us shokh ne mujhi ko sunaayi meri ghazal
poochha jo maine usase ki hai kaun khush-naseeb
aankhon se muskuraa ke lagaayi meri ghazal
ek-ek lafz ban ke udaa tha dhuaan-dhuaan
usane jo gungunaa ke sunaayi meri ghazal
har ek shakhs meri ghazal gungunaaye.n hain
‘Rahi’ teri zubaan pe na aayi meri ghazal
Sher: A sher is a two line stanza, it is a complete poem in itself. An important aspect is that each sher stands independently as a poetic thought and meaning of a sher does not require assistance of other shers in the ghazal. All shers in a ghazal follow a theme, but it is not necessary for them to be related to one another. A ghazal has at least five shers. Though the example above has only four shers.
Bahr: Bahr is a meter specifying the length and pattern of the lines in the sher, and there is a mechanism to measure it based on weight of each letter. Each sher in a ghazal, and each line in a sher must have same meter. There are 19 types of meters, and based on length classified as short, medium or long. I do not quite understand its complexities yet.
Radif: Second line of all shers in a ghazal must end with same phrase. In our example, this phrase is "meri ghazal", so ‘Radif’ for this ghazal is "meri ghazal".
Qaafiya: In each sher in a ghazal, words preceding ‘Radif’ must have same rhyming pattern. In the example above, words preceding "meri ghazal" are "sunayi", "lagayi", and "aayi", i.e. the Qaafiya is "…aayi".
Matla: The first sher of a ghazal is called ‘Matla’, and it must have ‘Radif’ in both lines. In our example, both lines of first sher end with "meri ghazal". A ghazal may have more than one ‘Matla’.
Maqta: Each shayar (poet) has a pen name. In the example above, it is ‘Rahi’ (other famous examples are Asadulla Khan ‘Ghalib’, ‘Mir’ Taqi Mir, ‘Daag’ Dehlvi, Ahmed ‘Faraz’). The last sher of a ghazal is called ‘Maqta’ and it must contain poet’s pen name.
In short, a ghazal is a collection of ‘Sher’ (couplets), containing one or more ‘Matla’, one ‘Maqta’; and all ‘Sher’ must be of same ‘Bahr’ (meter), and end with same ‘Radif’ and ‘Qaafiya’.