Initialism of institutional review board, a committee that reviews the designs of proposed experiments to confirm whether all the methods proposed are ethical.

(finance) Initialism of internal ratings-based approach

(historical) Initialism of Irish Republican Brotherhood, a secret organisation dedicated to the establishment of an "independent democratic republic" in Ireland between 1858 and 1924.

plural of IRB

A strait between Saaremaa and Courland in Latvia, connecting the Baltic Sea and the Gulf of Riga.

(pharmacology) An angiotensin II receptor antagonist used mainly for the treatment of hypertension.