A form of the sonnet that, as one may imply by its name, is much less structured than other sonnets. The only prerequisite of a free form sonnet is that it have fourteen lines. It does not require iambic pentameter, rhyme, or reason.

'Free form Sonnet' is a contradiction in terms. When I first learned of the sonnet, it struck me as being the most structured poetic template ever conceived by the mind of man. Apparently somebody decided that it was "too" structured, and watered it down.
For examples of real 'I was written by manly men wearing pantaloons' sonnets, see the Petrarchan Sonnet, the Spenserian Sonnet, and the Shakespearean Sonnet.

Reading/writing a Free Form Sonnet is like drinking decaf.

I was taught that a "free" "sonnet" needn't have 14 lines, but only approximately that amount. 13 or 15 is OK, 12 and 16 is pushing it, but any further . . .

As a writer, tho', I don't see the point.