Negative value for variable

I came across a game where variable is declared with negative value

selectedLevel:int = -1;
what does it mean

it means that the value is less than 0...

developers (read: "I") typically use negative values as -- generally binary -- semaphores.  This way I can essentially have a flag variable without the resource overhead of an actual additional variable.

in your example it logically means that "no level has _actually_ been selected, so don't run the level selection routines."