I DONT UNDERSTAND!!!!!

Question

In a code I was looking at it said this...

for(var i=0;i<trail.length;i++) {
ctx.fillRect(trail[i].x*gs,trail[i].y*gs,gs-2,gs-2);
if(trail[i].x==px && trail[i].y==py) {
tail = 5;

what the heck does that mean???