In law, a colloquy is a routine, highly formalized conversation. Conversations among the judge and lawyers (as opposed to testimony under oath) are colloquys. The term can be applied to the conversation that takes place when a defendant enters into a plea bargain and the judge is supposed to verify that the defendant understands that they are waiving their right to a jury trial.
In criminal court, a colloquy is an investigation within a defendant's plea to reassure that the plea was given knowingly, voluntarily, and intelligently. Defendant needs to understand the charges against him, the penalties that he will face, and his rights before entering into a guilty plea. In the United States, that includes describing the rights guaranteed by the 5th and 6th Amendments as well as a caution that non-citizens who are convicted of crimes risk expulsion from the country.
A Defendant who denies guilt may still "plead down" (lesser offense than accusation) but: 1) Provided Court allows it. 2)Provided accused intelligently concludes on an open record that a plea is in her/his best interest. (e.g. avoiding incarceration, a more serious charge/convicton).