The Stall is the period of time while you are smoking meat that the internal temperature stops rising and holds or even slightly drop for up to several hours.
For the backyard BBQ enthusiast who is cooking a brisket or pork butt for the first time this can be very confusing/frustrating. So relax… this happens to everyone… you did not screw anything up… and do not raise your cooking temps – you must wait the STALL out.