Free verse and blank verse

These terms are often misunderstood:
Free verse has no set rules such as specified length of line or rhyme. The poet and reader must pay attention to such aspects as natural rhythm, effectiveness of having some short and some longer lines and use of unregulated length of stanzas.
Blank verse has no rhyme but does have a formalised line length of five iambs and is therefore in unrhymed iambic pentameters. An iamb is a two-syllable unit with the weak stress first and the heavy stress second as in the word again. A line of blank verse follows the rhythm of five repetitions of this word: again, again, again, again, again. Much of Shakespeare's verse is written in iambic pentameters as are true sonnets.
Sometimes, particularly at the beginning of a line, the first foot may be inverted with the stress on the first syllable. A foot is the name given to each unit when the line is analysed and so an iamb is an example of a foot.