Haiku, the well-known Japanese poetic form, consists of three lines; each line must have the correct number of syllables. Due to differences in language, in English this is roughly translated as five syllables in the first line, seven in the second and five in the third. Haiku poems do not necessarily rhyme. A tanka, a five-line form that uses more figurative language than haiku, has a similar structure. The lines of a tanka must have, sequentially, five, seven, five, seven and seven syllables.
Acrostic poems are formed from the first letters of consecutive lines, which spell a word vertically. This word is generally the subject of the poem. Acrostics are also known as alphabet poems. Rhyming is not necessary in an acrostic poem. In some acrostic poems, the first line of the poem also may be the word that is spelled vertically.
A cinquain is a poem with five lines. Each line follows one of two sets of rules. Each line must have a certain number of syllables or words. If counting words, then the first line must have one word, the second has two words, the third has three words, the third has four words and the fifth has one word. If counting syllables, there must be two syllables in the first line, followed by lines with four, six, eight and two syllables, sequentially. Cinquains do not need to rhyme.
Diamonte or diamante poems are named after their diamond shape. These poems have seven lines and must follow grammatical formulas to be accurate to the form. The first line is usually the subject. The next line uses two adjectives to describe the subject. The third line is three verbs, and the fourth line has four nouns related to the subject. Line five has three more verbs, line six has two more adjectives, and the last line is a synonym for the subject of the poem.
Free verse poetry generally has no rules, leaving it open to the individual poet's creativity. Usually, free-verse poems are recognized by their lack of structure and rhyme. These poems can use poetic devices, but unlike other forms of poetry, they are not obliged to do so. This form of poetry is somewhat controversial due to its lack of rules and structure. Robert Frost compared free verse to playing tennis with the net down.