An allocution, or allocutus, is a formal statement made to a court by the defendant who has been found guilty before being sentenced.
The defendant explicitly admits specifically and in detail the actions and their reasons in exchange for a reduced sentence.
The term allocution is used generally only in jurisdictions in the United States, but there are vaguely similar processes in other common law countries.
In many other jurisdictions, it is for the defense lawyer to mitigate on their client's behalf, and the defendant rarely has the opportunity to speak.
It is generally phrased as: "Prisoner at the Bar, you have been found Guilty by a jury of your peers of the offence of XYZ.