Murder is the only crime where a mandatory life sentence is automatically imposed but it can be imposed on a variety of other serious crimes including but not exclusively manslaughter, rape and other violent crimes.
Subsequently a tariff is set which mean the offender is given a specific number of years they have to serve in prison before they can be considered for release.
The tariff, or number of years, is decided by a variety of factors including the seriousness of the crime.
Someone convicted of a double murder, or a particular cruel or vicious murder would have their tariff set at a higher range then a lesser crime.
Factors that may reduce the tariff include: if the offender plead guilty as soon as possible, saving the victim, or their families the ordeal of a court case, whether they had shown remorse, or if the offence was committed in the heat of the moment.
Circumstances exacerbating the tariff set include: the amount of violence used in the offence, whether the victim was particularly vulnerable or if the offender fled the scene of the crime.
Whole life sentences
Whole life sentences are extremely rare and only imposed on the most serious category, or for repeat offenders.
Some people convicted of murder who are released and go on to re offend can be handed whole life terms.
Trevor Hamilton was the first person in Northern Ireland to be given a whole life sentence for a non-terrorist related offence.
Four months after he was released from prison for another rape, Hamilton murdered a 65-year-old woman as she made her way home from Mass in Strabane.
In 2008 his sentence was reduced to 35 years on appeal.
Convicted killers Jeremy Bamber, Peter Moore, Douglas Vinter and two others are to ask the European Court of Human Rights to rule on whole life sentences.
In a separate case in 2008 the UK's Court of Appeal found whole life sentences did not constitute cruel or inhuman treatment.
Currently whole life tariff prisoners stand virtually no chance of release as their offences are so serious.
Only the secretary of state can free them on compassionate grounds if the prisoner is terminally ill.
A total of 41 inmates are serving whole life sentences in England and Wales.
Scottish judges do not have the power to hand out whole-life sentences.
Interdeterminate sentences have been introduced fairly recently in Northern Ireland, but have been used consistently in England and Wales for much longer period of time.
These sentences are usually given to the most dangerous offenders.
For example someone who has a string of previous convections for offences like grievous bodily harm who then goes on to commit an armed robbery.
They also allow a variety or parameters or conditions to be placed on the defendant.
The judge may give them an indeterminate sentence but state they must serve a minimum number of years before they are eligible to have their release date reviewed.
Or if they are released, it may be under very strict or specific licence terms.
Initially they may be eligible to be released one or two days a week.
If their offence involved alcohol or drugs a condition of them being out on licence could involve avoiding the substances or taking regular tests.
Extended custodial sentence
An extended sentence is any time an offender spends in prison after they have met their minimum tariff.
If after they complete their original tariff they are not eligible for release a further review date will be set.
This is usually done when offenders are still seen to pose a threat to society or if they have continued to re-offend
By Natalie Lindo BBC News