Illegal Sentence Law and Legal Definition
An illegal sentence is one imposed after a valid conviction, but not authorized by law. For example, a sentence in excess of that imposed by statute, or imposition of an unauthorized form of punishment. Motions can be filed to correct an illegal sentence.
Example of a state law ( Texas) on illegal sentence.
In Texas, the state is entitled to appeal a sentence in a case on the ground that the sentence is illegal.[ Tex. Code Crim. Proc. art. 44.01]