What is Eminent Domain?

Earlier this week, I posted a news article on Howard County tabling eminent domain. So, what is eminent domain? Black's Law Dictionary, 8th edition, defines eminent domain as "The inherent power of a government entity to take privately owned property, esp. land, and convert it to public use, subject to reasonable compensation for the taking." Black's quotes John E. Nowak and Ronald D. Rotunda's Constitutional Law :

The term 'eminent domain' is said to have originated with Grotius, the seventeenth century legal scholar. Grotius believed that the state possessed the power to take or destroy property for the benefit of the social unit, but he believed that when the state so acted, it was obligated to compensate the injured property owner for his losses. Blackstone, too, believed that society had no general power to take the private property of landowners, except on the payment of a reasonable price. The just compensation clause of the fifth amendment to the Constitution was built upon this concept of a moral obligation to pay for governmental interference with private property. (quoting Bauman v. Ross, 167 U.S. 548, 574, 17 S.Ct. 966, 976 (1897).