"Nolo contendere" is a pleading, verbally tranlated from Latin it means: "I do not wish to contest" the charges.
It basically has the same consequences as pleading guilty has, but the difference is that it is not an admission of guilt and therefore cannot be used in a subsequent civil trial.
Example: I am charged with criminal assault, meaning I am charged with hitting the victim over the head. I plead no contest. There is enough evidence to convict me anyway.
The victim will also sue me in civil court for the tort of battery, which is the unlawful harmful touching of a body of another. If I had plead guilty in criminal court he could now say: look, he admitted already that he did it. Since I pleaded "no contest" the victim needs other evidence to have me convicted for battery.
In practice such an example would not make much sense, since usually it is more difficult to convict someone of a crime than of a civil tort (two different standards of factfinding). If the DA had enough evidence to convict me in criminal court, very probably the victim will have enough evidence in civil court, too.
In othe rcircumstances it might become interesting, as someone here already mentioned immigration law, though the courts there also see "no contest" and "guilty" more and more as being the same.
