Definitions of extended sentence
a prison sentence that has been made longer than the original length of time in jail given as a punishment, for example if a former prisoner commits a further crime while released on probation
He was given two-and-a-half years in October but had his sentence extended after the same judge gave him a further 16 months for another blackmail offence.
a prison sentence that is longer than the usual sentence given as a punishment for that particular crime, usually because the convicted criminal poses a significant risk of serious harm to the public. In the UK, an extended sentence comprises a normal prison sentence and an extended period of time on licence (=a form of temporary or conditional release form prison).
I will impose an extended sentence of 18 years. The custodial element will be nine years.