An offender is, in legal practice, a person who has committed a criminal offence, ordinarily established by conviction. The term is used mainly post‑conviction in courts, sentencing, probation and offender management. Before conviction, practitioners should use suspect, accused or defendant, not offender, in line with the presumption of innocence.There is no single universal statutory definition; offender is a descriptive expression used across criminal justice legislation and case law. Specific schemes define it for particular purposes, for example: relevant offender for sex‑offender notification requirements (under the Sexual Offences Act 2003 and cognate legislation; Sex Offenders Act 2001 in Ireland); dangerous offender for risk‑based sentences (Criminal Justice Act 2003 in England and Wales; Criminal Justice (Scotland) Act 2003 orders for lifelong restriction; Criminal Justice (Northern Ireland) Order 2008); and persistent or repeat offender in sentencing guidance. Young offender generally denotes under‑18s within youth justice systems, though terminology varies.Practically, classification as an offender determines court jurisdiction, sentencing powers (custody, community orders), ancillary orders (e.g. Sexual Harm Prevention Orders, restraining orders), probation supervision, risk assessment and notification, and disclosure/rehabilitation periods (Rehabilitation of Offenders Act 1974 and analogous regimes). Usage is broadly consistent across England & Wales, Scotland, Northern Ireland and Ireland.