What is the form of a poem?

In poetry, form is the physical structure of the poem. When a poet makes a decision about form, he is prescribing himself to carry both an internal and external baggage. Internal baggage comes in the form of following certain rules of structure, metre, rhyme, punctuation, repetition and tone. For example, if a poet chooses to write in the form of a sonnet, he must aim to write 14 iambic pentameters, with a choice of rhyme scheme reflecting different ways of structuring the lines. External baggage exists because forms have become historically associated with particular ideas and concepts throughout history. For ex\ample, sonnets have served as love poems and in courtship throughtout history, and as such, are thematically expected to be about love and romance.