Blank verse is unrhymed poetry with each line having the same meter - that is each line has the same number of syllables with those syllables creating a regular rhythm.    

Although free verse requires no meter, rhyme, or other traditional poetic techniques, a poet can still use them to create some sense of structure. A clear example of this can be found in Walt Whitman's poems, where he repeats certain phrases and uses commas to create both a rhythm and structure.

Something there is that doesn't love a wall, 
That sends the frozen-ground-swell under it, 
And spills the upper boulders in the sun, 
And makes gaps even two can pass abreast.

         First four lines of "Mending Wall" by Robert Frost