Definition of Plea
A plea is a defendant's answer to a formal charge against them. Pleas can include guilty, not guilty, no contest, or failure to enter a plea. A guilty plea is an admission of guilt. A not guilty plea is a denial of the charges. A plea of no contest, while not an admission of guilt, means the defendant is not contesting the charges. Consider, however, that if you make a no contest plea you will generally be treated as if you were guilty and you may be immediately sentenced and will not be able to defend the charges in court.
Generally, a plea is made by the defendant at the arraignment. If you have been charged with a crime it is a good idea to discuss your case with a criminal lawyer before attending the arraignment. For some types of charges you will be required to appear in court to make a formal plea. Other cases such as misdemeanors may allow your attorney to appear in court for you and make your plea.