Definition
An attempt to find out information about something by collecting a lot of data, often in a secretive way.
The newspaper reporters conducted a wide investigation into the politician's background, but ultimately, it turned out to be a fishing expedition to dig up dirt.
Without clear evidence, the police interrogated all the employees; it was essentially a fishing expedition to gather information.
The company launched a wide review of its competitor's patents; it was clearly a fishing expedition to find any loopholes they could exploit.