Hostage, a person held in captivity to assure that an agreement is observed or to coerce another party into taking (or not taking) some action. Countries in ancient and medieval times sometimes exchanged hostages, often persons of high rank, who could be put to death if certain agreements were broken. Invading armies often take hostages of local citizens to discourage resistance to their occupation. Terrorists sometimes seize hostages both to force concessions from governments and to gain publicity for their cause.
The best form of riot control is prevention: Often, a passive but strong police presence can keep a "gathering" from turning into a "riot." But sometimes, a spark ignites a flame. Learn how police and military forces handle a riot.
Say you're a government agency or a company of some sort and you want to negotiate the terms of a working relationship with another group or agency. However, you're not too enthused by the idea of lawyers, contracts and legalese. That's where Memoranda of Understanding come in. What are these MOUs, exactly, and who uses them?