Illegality, the Criminal Procedure Code, 1898 does not use the word 'illegality'. Even defects or violations that vitiate the proceedings and render them void are spoken of only as irregularities in
s. 530. The word illegality was used almost for the first time in the judgment of the Privy Council, LR 28 Indian Appeals 257 (familiarly known as Subramania Aiyar's case), where they speak of a contravention of s. 234 of the Code, resulting in a misjoinder of charges, as an illegality, Willie (William) Slaney v. State of Madhya Pradesh, AIR 1956 SC 116 (134): (1955) 2 SCR 1140.
The Criminal Procedure Code, 1973 does not use the word 'illegality', nor defines 'irregularity' and illegality can only mean an incurable illegality, incurable because of prejudice leading to a failure of justice, Bhoor Singh v. State of Punjab, AIR 1974 SC 1256 (1261): (1974) 4 SCC 754.
Means an act that is not authorised by law, Black's Law Dictionary, 7th Edn., p. 750.