A blighted area is basically an area that is considered to be an eyesore.
Examples of blight are, abandoned cars, Abandoned Vehicles, Run down homes, Trash or Junk in yards, Overgrown Grass, Tall weeds in the yard and a whole lot of other things could be considered blight.
Even graffiti on buildings or vehicles or anywhere else can be blight and cause a blighted area.
Blighted areas can increase the chance that Violence or other Illegal activity such as drugs could occur in that area.
Blight also brings down your and other peoples property Values and makes it hard to sell your house should you decide to sell the place in the future.