Prisoners, in the simplest, most general use of the term, are persons incarcerated under legal proceedings addressing violations of public law. The facilities that incarcerate prisoners likewise can be simply and generally termed prisons. Prisoners and prisons are the best terms in English to use for general, transnational discussions of justice systems.
Prisoners, prisons, and other terms of incarceration are complicated by more specific and exclusive usages. For example, in the U.S., the term “prisoner” often is used specifically for persons confined in justice-system institutions that federal and state governments operate. The term “inmate” often is used for persons confined in locally or regionally operated incarceration facilities. “Prison inmate” or just “inmate” is also sometimes used for persons confined in federal and state facilities. “Inmate” historically has also been used for residents of other public institutions such as hospitals and asylums. “Convict” is an older term typically used for a person sentenced to years of incarceration.
The specific uses of prisoner and inmate typically parallel distinctions among incarceration facilities. In the U.S., “prison” is often used for an institution holding persons sentenced to a year or more of imprisonment. Jails and police lock-ups hold arrested persons before booking. Jails, but usually not police lock-ups, hold pre-trial detainees, persons awaiting sentences, and persons serving sentences typically of less than a year. Despite the difference in the specific usage of the terms “prisoner” and “inmate,” the distinction between prisons and jails is not well-defined within the U.S. For example, Hawaii, Alaska, Vermont, Rhode Island, Connecticut, and Delaware do not distinguish between jails and prisons. The federal justice system operates pre-trial detention facilities analogous to local jails. The distinction between prisons and jails is also not generally applicable internationally.
Confusion in incarceration terms reflects historical cross-currents in ideas about the status of incarcerated persons and the purpose of incarceration. Early modern incarceration facilities for high-status persons (treacherous nobles, heretical high clergy, etc.) were called “prisons”. Incarceration facilities for low-status persons were called “workhouses,” “houses of correction,” and “jails.” Late in eighteenth-century England the idea of a “penitentiary” developed. Penitentiaries were incarceration facilities designed to foster repentance for crime. The rise of social science in the nineteenth century prompted the establishment of “reformatories.” These institutions sought to reform persons through the operation of professional treatment expertise. The term “detention center” emerged in the twentieth century as an abstractly functional description for a short-term incarceration facility. “Correctional institution” is a modernization of “house of correction” unmoored from a belief in the possibility of correcting persons. Penitentiaries similarly continue to exist without belief in the significance of penance.
Incarceration terms must be interpreted in the context of their use and with broader knowledge about how the relevant justice system disposes persons. Where are persons immediately after they are arrested? Where are persons before a trial, between court appearances (remanded), awaiting sentencing, and serving sentences? How are persons within the community but under criminal justice supervision, e.g. probation and parole, counted within justice system statistics? A key step to understand is asking questions, even if only to yourself.