Mimi Khalvati, whose poem 'Ghazal' is the only poem so far to use a ghazal form in the Archive, defines it at the start of her reading of it: "Ghazals are an old Persian form, and they're written in self-contained couplets with a monorhyme, sometimes one- (or two- or three-) word repeated phrase, like a refrain, and the last couplet is a signature couplet, in which the writer has to refer to themselves by name, or pseudonym, or by using some kind of wordplay on their name." In her ghazal, the repeated word is "me", the rhyme is on "through", "woo", "cue", "tattoo" and so on, and the 'signature' is in the reference to being "twice the me", or 'Mimi'.
Like the haiku, the age of the form - the ghazal can be traced back through a millennium - and its translation into the English language mean that the 'rules' have had significant variations over time. You may find some definitions insist that the subject of a ghazal should be love, and others that let the rhyme move to be earlier in the line than Khalvati's placement of it immediately before the refrain. Some insist that each couplet should be complete in itself, meaning that each stanza ends on a full stop, and can therefore have only a thematic connection to those either side. There are even some that do without the refrain, but these appear rare. The closed couplets, however, appear to be a necessity to the form.