Looks like the white streak extends into the menubar, so it's part of the screen? That would appear to be a pressure crack (permanent damage), or just scratches (although the scratches would be the same result as a pressure crack.)
The LCD panel is manufactured in multiple layers. A relatively minor break from too much pressure may just go into the first layer, and just give you a little light bleed, without the major leakage, or crosshatch/plaid-looking pattern characteristic of a bad crack through multiple layers.
The fix either way is replacing the LCD panel.
Although you say you haven't dropped your MBAir, you may have dropped something across the screen. I've seen something like that happen in a book bag when when someone sat on the bag.