A fishing expedition is an informal, pejorative term for a non-specific search for information, especially incriminating information. It is most frequently organized by policing authorities.
Media
In the United Kingdom, Abu Hamza al-Masri and Yaser al-Sirri, Jim Davidson, and the late Edward Heath were described in the media as having been subjected to this tactic.
Former friends of the late prime minister Edward Heath complained that Mike Veale, Chief Constable of Wiltshire Police, had mounted a 'fishing expedition' in an 'unsatisfactory and prejudicial' investigation costing £1.5 million which had turned up 'no convincing evidence' that Heath had ever sexually assaulted anyone, according to Lord Hunt of Wirral.
Law
In pre-trial procedure, so-called "fishing expeditions" are massive and aimless calls for all documents related to the litigation: in the United States they are permissible under Federal Rule of Civil Procedure 26 (b) (1). This rule is repeated in many states' rules of procedure: "Parties may obtain discovery regarding any matter, not privileged...