What does structured verse mean?

Free Verse:
So much depends
upon a red wheelbarrow

glazed with the rainwater
beside the white chickens.

Structured:
Once upon a midnight dreary, while I pondered weak and weary,
Over many a quaint and curious volume of forgotten lore.
While I nodded, nearly napping, suddenly there came a tapping,
As of someone gently rapping, rapping at my chamber door.
"Tis some visitor," I nodded, "tapping at my chamber door."
Only this and nothing more.

Thus saying, free verse just tends to be whatever you want- doesn't necessarily have any structure other than flow, and it doesn't have to have a rhyme scheme. Structured, however, does, whether you want a quatrain, a Sonnet, etc.