Bail is to set free or liberate a person arrested or imprisoned on taking security for his appearance. 

The basic conception of the word "bail" means release of a person from police custody and delivery unto the hands of a surety who undertakes to produce the accused in Court whenever required to do so. Therefore, a person to be released on bail need to be in some sort of confinement or custody or oth­erwise it is not understood from what confinement or custody he would be released. (Abdus Samad & others Vs. State, 1989, 18 CLC (HCD) [6304])

The prohibition under the law is that a person accused of any non-bailable offence shall not be released on bail if there is rea­sonable ground for believing that he is guilty of an offence punishable with death or im­prisonment for life—Section 497(1), the Code of Criminal Procedure, 1898 (V of 1898). (Shaikh Shahidul Islam Vs. The State 13 BLD (AD) 190)

Basic conception of the word ‘bail’ is release of a person from the custody of police and delivery in the hands of sureties, to undertake to produce him in court whenever required to do so. (Crown Vs. Khushi Md. (1953) 5 DLR (FC) 143 (150))

See also Anticipatory bail.