A Special Assessment District (S.A.D.) is a geographic area in which the market value of real estate is enhanced due to the influence of a public improvement and in which a tax is apportioned to recover the costs of the public improvement.
Void, voidable, and unenforceable contracts: (1) A void contract is one without any legal effect from the beginning. (2) A voidable contract is one that a party may elect to avoid or ratify. (3) An unenforceable contract is one otherwise valid but for which some defense exists extraneous to formation.
An example of a transaction which is an unenforceable contract is a contract for prostitution under English law. Prostitution is not actually a crime under English law, but both soliciting a prostitute and living off the earnings of a prostitute are criminal offences.