What free verse claims to be free from is the constraints of regular metre and fixed forms. This makes the poem free to find its own shape according to what the poet - or the poem - wants to say, but still allows him or her to use rhyme, alliteration, rhythms or cadences (etc) to achieve the effects that s/he feels are appropriate. There is an implicit constraint, however, to resist a regular metre in free verse - a run of a regular metre will stand out awkwardly in an otherwise free poem.
Sometimes known as vers libre, free verse has a long pedigree and is very common in contemporary poetry. Yet there are still voices that claim poetry is only poetry when it is formal verse, and would agree with Robert Frost who, when asked about free verse, said "I'd just as soon play tennis with the net down". Fans of free verse can counter with T S Eliot's insistence that "no vers is libre for the man who wants to do a good job" - the net may be down, but this allows a poet (of either gender) to play to different rules. Simon Armitage's 'You're Beautiful', for example, creates for himself a set of rules that includes repeated words at the starts of phrases, rather than a structure of repeated sounds at the end of lines.