Definition of "IRB"

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

Initialism of investment review board, a committee of business executives who review investment choices, comparing against strategy and opportunity costs.  examples

Initialism of internal review board, an internal affairs division of a police department.  examples

(finance) Initialism of internal ratings-based approach  examples

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

(rugby, historical) Initialism of International Rugby Board, the name used by World Rugby, the worldwide governing body for rugby union, from 1998 to 2014.