Legality of torture

The South Park - thread led me to think about the definitions behind torture and the legality of it. Allegations have been made that torture is allowed in a war situation. There often is no governing body to oversee that no torture takes place in war situations making these torture bans pretty useless.

The Geneva Convention has been mentioned and that it allows certain torture methods while not allowing others. Individual countries may have even stricter laws prohibiting torture and I think Finland's laws are pretty strict when it comes to torture and general mistreatment of prisoners. The idea of looking for loop holes in a law that bans the use of torture makes me wonder if a country that actively does that and uses torture really would qualify as a western civilized nation.

Questions: What is torture, is prison (the taking away of freedom of movement) torture in itself? Is water torture torture or is it just 'mild' torture? The US has allowed the use of water torture until it was banned recently, is the ban working? How does the public know if torture is being used or not? How do we know what forms of torture have been used by the US and other nations?