Something you obsess over to the point that it nearly or completely destroys you. An obsession that becomes your ultimate goal in life; one that your life now completely encircles and defines you.
Captain Ahab was so obsessed with killing Moby Dick (the white whale) that it in turn killed him.

The desire to be thin became her white whale. Through diet pills, starvation, vomiting, and obsessive exercise, she was determined to be skinny.
by Articulate Austinite December 28, 2011
A white whale is something you cant get seeing a white whale would be rare. It would be seeing something you always wanted and you absolutely have to buy it. So when u get it, it's your white whale.
I have yet to find my white whale. It will be a great day when I do though.
by Cool Breez February 2, 2005
When one's 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 friends, explain the legend of the mysterious white whale that is rumoured to live at the bottom of the lake. Dive down in search of the beast, wait 10 sec., execute the manoeuvre described above
by The Hawk August 25, 2005
a slang term for a large white female. commonly used by young men but also other groups.
duuude! that guy is dating a white whale. what a chubby chaser.
by jimjam87 July 1, 2010
When you are face fucking a chick, pull out after you fill their mouth with semen, then proceed to slap both of their cheeks at the same time yielding the same appearance of a whale surfacing for air.
If you can't figure it out from the definition of white whale then you are too fucking stupid.
by Wayne Sucks July 7, 2009
When someone is sleeping and you croutch over top of them, pull down your pants, place your butt cheeks close to their face, then slap them across the face to suddenly wake them up and cause them to jump up into your ass....if a well executed white whale is performed the nose will directly hit the anus. Note: the person giving the "whale" is white (caucasian), otherwise it is known as a "black" whale (or substitute according to ethnic background and ass color)
My college roomate was sleeping on my couch, so I decided to give him a white whale.
by J-Vizzle September 1, 2006
Term used to describe an opponent/nemesis who is extremely difficult to defeat. The term can also apply to miscellaneous games or events which are difficult to master.
The USC Trojans, although indisputably the most talented team in the PAC 10, always struggle against the undermanned Oregon State Beavers. One can surmise that the Beavers are the Trojans' White Whale.

Isaac has not beaten Jamal in a 1-on-1 basketball game in the last 20 tries. Jamal is his White Whale.

Baron excelled at video games as a child, although he was noticeably deficient at Guitar Hero, struggling to even play Medium Level songs. After many miserable bouts with failure, he conceded that Guitar Hero was his White Whale, the one game which he could not overcome.
by Z_19 September 14, 2009