A cold war is a state of conflict between nations that does not involve direct military action but is pursued primarily through economic and political actions, or conflict through surrogates. The surrogates are states that are "satellites" of the conflicting nations, i.e., nations allied to them or under their political influence. It also involves conflict on a covert level, through acts of espionage.
The term entered usage during The Cold War, which was such a state of tension between the western and the eastern countries between 1950 and 1990, particularly between NATO and the countries of the Warsaw Pact. Except for the Korean War, Vietnam War and the conflict in Afghanistan, the aggression between those two parts of the world never shaped in an armed conflict, but was conducted by or against surrogates and through spies and traitors which were working undercover. In each of those conflicts, at least one of the major powers operated mainly by arming or funding surrogates. Because of that, the population of the major powers were rarely directly impacted by this "war". Also, the armies of the countries involved rarely had much participation in the Cold War; the war was primarily fought by intelligence agencies like the CIA (United States), MI6 (Great Britain), BND (West Germany), STASI (East Germany) and the KGB (USSR). The major world powers never entered armed conflict directly against each other.
Many observers today think that the United States acted in ways their own constitution and national sentiment would not support. Leaders in the U.S., both political and military, commonly cite the perceived threat to their security as justification for their actions. In many areas of the world, the local populations feel they were manipulated and abused by both powers. Much of the anti-Americanism in countries such as Afghanistan is attributed to the actions by the U.S. During the Soviet conflict with Afghanistan, the U.S. funded and armed the Mujahedeen in their fight to repel the Soviet occupation, but pulled out and left them to fend for themselves once the USSR had pulled out of the region.
Beyond the actual fighting and killing that went on through intelligence services, the Cold War was heavily manifest in the concerns about nuclear weapons and the wars which could be fought with them, as well as in the propaganda wars between the United States and the USSR. It was far from clear, going through these times, that global nuclear war would not result from the smaller arenas of conflict, giving each of them an added degree of concern. These pressures impacted many aspects of life throughout the world, much more so than the actual fighting going on between intelligence services.
One major hotspot of conflict was Germany, particularly Berlin. Arguably, the most vivid symbol of the Cold War was the Berlin Wall, isolating West Berlin (the portion controlled by West Germany and allied with France, England and the United States) from East Germany, which completely surrounded it. Many East Germans risked death attempting to cross the defenses surrounding the wall to reach freedom in West Berlin, and many were killed in the attempt. President Ronald Reagan's challenge "Mr. Gorbachev, tear down this wall!" in 1988 seemed mere grandstanding, yet the wall was torn down within two years -- not by Premier Gorbachev's order, but by the citizens of East and West Berlin.
The Cold War also inspired a lot of movie-companies and writers, resulting in an enormous amount of books and movies which tell about the cold war, some more fictional (James Bond) some less.