Any person actually detained or subject to detention in custody whose release may lawfully be effected by bail is defined as a?

The correct answer is that a person actually detained or subject to detention in custody whose release may lawfully be effected by bail is defined as an arrestee.

In the context of bail practice, the term "arrestee" specifically refers to an individual who has been taken into custody by law enforcement and is awaiting legal proceedings. This definition directly relates to the eligibility for bail, as an arrestee is the person from whom bail can be requested to secure release pending trial or other legal processes.

While "defendant" refers to an individual who has been formally charged with a crime and is facing prosecution, that designation typically applies after the initial arrest. The term "criminal" is broader and often relates to someone who has committed a crime, but does not specifically define their status regarding detention or bail eligibility. The inclusion of all options in the list isn't accurate since only the term arrestee specifically addresses the condition of being held in custody and having the possibility for release through bail. Thus, the focused definition of arrestee makes it the clear and correct answer in this context.