Definition: Free verse poetry doesn't have to rhyme or to have much reason about it. This style of poetry can be about anything, anyone, any place or any thing that the author would like to express. Often times, lyric poetry can be considered free verse. Rap is a popular style of music or lyrical poetry that can also be included in the free verse style of poetry.(Rap often doesn't follow any rules and doesn't always rhyme.)
Many of us might feel that free verse (or verse that has no strict metrical pattern, line length, or rhyme scheme) is the most expressive kind of poetry. It can be very expressive indeed. But very often free verse isn't so free. It is usually the case that the poet wants the reader to hear something in a different way, or to think about something in a different way. Poets may use free verse to get our attention; but usually, free verse can use a variety of rhythms, rhymes, sounds, and line lengths to force us to attend to the language in different ways.
Poetry that is based on the irregular rhythmic CADENCE or the recurrence, with variations, of phrases, images, and syntactical patterns rather than the conventional use of METER. RHYME may or may not be present in free verse, but when it is, it is used with great freedom. In conventional VERSE the unit is the FOOT, or the line; in free verse the units are larger, sometimes being paragraphs or strophes. If the free verse unit is the line, as it is in Whitman, the line is determined by qualities of RHYTHM and thought rather than FEET or syllabic count.