Longman Dictionary of Contemporary English
Wikipedia
A custodial sentence is a judicial sentence, imposing a punishment (and hence the resulting punishment itself) consisting of mandatory custody of the convict, either in prison or in some other closed therapeutic and/or (re)educational institution, such as a reformatory, (maximum security) psychiatry or drug detoxification (especially cold turkey). For some crimes, such as cases of child sexual abuse, a custodial sentence is almost inevitable.
Although usually not labeled as such (at hence not in the legal sense) it can be considered a type of corporal punishment, even if no further physical punishments are practiced within the institution (these can also be informal, without any rights of defense), since it constitutes a physical coercion. Indeed the technical term duress is equally used for loss of liberty and for coercion.
The concept of penal harm often induces additional elements of physical endurance.
Every other sentence and punishment is non-custodial, such as fines, judicial beatings, various mandatory but 'open' therapy and courses, restriction orders, loss or suspension of civil rights, or even suspended sentences.
Usage examples of "custodial sentence".
The Surgeon-Captain is an ethical and highly moral being who would consider it dishonorable to escape what it will consider to be a justly imposed punishment for its crime by means of suicide, even though a custodial sentence would be the harshest, in terms of continued mental distress, that could be imposed.
On the third occasion, the court decided not to give him a custodial sentence, on the condition that he move to Manchester to live with Peggy and her husband Patrick Brady.
The Inspector happened to catch sight of a man who had served a single custodial sentence, and immediately suspected the worst, and acted on that suspicion - quite wrongly, as it turned out.
He'd been lucky though, landing more than his fair share of fines and tickings-off when a custodial sentence might have been more usual.
Peter was to neither approach nor contact Polly for an indefinite period, and should he try to do so he risked a custodial sentence.
That sense of humour was doubtless painfully tested when the less-than-understanding sheriff imposed a custodial sentence, but for McGregor at least it seemed to draw some kind of line under the matter.
Justice Erskine-Brown (PhillidaTrant as she was in happier days when I called her the Portia of our Chambers), still possessed of a beauty that would break the hearts of the toughest prosecutors and make old lags swoon with lust even as she passed a stiff custodial sentence.