According to the search results, "white whale" has different meanings depending on the context. Here are the different meanings:

• Urban Dictionary: According to Urban Dictionary, "white whale" refers to a situation where ones nude buttocks breach the surface of the water, allowing a discharge of stale poo gas to be expelled in a spray of fine mist. While swimming with others, this can be embarrassing and unpleasant for everyone involved.

• Obsession: The phrase "white whale" can also refer to an obsession that is dangerous to an individuals safety and/or health. It is used to describe an activity or thing that an individual obsesses over and/or is constantly chasing to the point that it becomes dangerous for their health or safety. The white whale is an individual’s ultimate goal, according to Urban Dictionary. It is derived from the story of Moby Dick, where Captain Ahab was obsessed with hunting and killing the white whale, Moby Dick.

• Money laundering operation: "White Whale" is also the codename given by Interpol and EUROPOL for an international money laundering operation near Costa del Sol, Kingdom of Spain. The operation began in September 2003 and concluded with a massive crackdown on the money laundering network.

Therefore, "white whale" does not have a specific meaning in police.