A wide ranging social theory roughly stating that problems, if not dealt with as soon as they occur, become much worse than they would otherwise be.
The usual example given is the broken window in a neighborhood. If the window is not fixed as soon as possible, the bad element (whatever that is for that neighborhood) surmise that no one cares so they move it. Conversely, if it is fixed immediately, the bad element knows that people are aware and active in the neighborhood.
See also Ruin Porn.
This bit of jargon has been viewed 38,914 times.