What is Twelve Tables?

Legal Definition
According to Roman tradition, the Law of the Twelve Tables (Latin: Leges Duodecim Tabularum or Duodecim Tabulae) was the legislation that stood at the foundation of Roman law. The Tables consolidated earlier traditions into an enduring set of laws.

The Twelve Tables are sufficiently comprehensive that their substance has been described as a 'code', although modern scholars consider this characterization exaggerated. The Tables were a sequence of definitions of various private rights and procedures. They generally took for granted such things as the institutions of the family and various rituals for formal transactions. The provisions were often highly specific and diverse, and lack an intelligible system or order.
-- Wikipedia
Legal Definition
The earliest statute or code of Roman law, framed by a commission of ten men, B. C. 450, upon the return of a commission of three who had been sent abroad to study foreign laws and institutions. The Twelve Tables consisted partly of laws transcribed from the institutions of other nations, partly of such as were altered and accommodated to the manners of the Romans, partly of new provisions, and mainly, perhaps, of laws and usages under their ancient kings. They formed the source and foundation for the whole later development of Qoman jurisprudence. They exist now only in fragmentary form. See 1 Kent, Comm. 520.
-- Black's Law Dictionary
Legal Definition
The name given to a code of Roman laws, commonly called the Law of the Twelve Tables. (q. v.)
-- Bouviers Law Dictionary