A custodial sentence is a court judgment in a criminal case, wherein the judge sentences the defendant to incarceration time.
The time spent incarcerated is referred to as time spent in custody, so the custodial sentence is the amount of time that the defendant is ordered to spend in jail for any particular crime.
Custodial sentences are always the result of a criminal case, and the length of each custodial sentence can vary if the person is sentenced under a common law.
If the person is sentenced under a statutory law, the custodial sentence will be predetermined in length and therefore be the same for each defendant charged with that crime.
Once a defendant is serving a custodial sentence, they may be subject to allowances by the prison system, which allows for a reduction in the time spent under the terms of the sentence.