Courtesy cut-off

The act of making a lane change in a moving vehicle, while placing your turn signal on for one, but no more than two blinks to alert the other driver that you are in the process of cutting them off.

You need to make a lane change; however, if you place your turn signal on for too long other drivers will not let you in the lane.

Instead, you check to see that you can get into the lane, place your turn signal on, and immediately possess the lane. Therefore, giving the other driver a courtesy heads up that you are cutting them off. Hence, courtesy cut-off.