As stated by others here, tip stall is simply that. The tip of the wing stalls prior to the remainder of the wing and usually results in loss of control or almost such. 1/1 scales are usually designed with either significant outer wing washout or a symmetrical tip section with a much more lifting section at the root, usually progressive from the root, along the wing span, to the tip. this places the inner wing sections at a higher angle of attack thus normally initiating the stall at the root section then outward from the wingroot.

While most here relate the problem to landing approaches, I have witnessed many heavy (relatively speaking of model airplanes) "War-Birds" bite the dust ON TAKE-OFF because the RC pilot tried to fly it like a Q-500 or some easy taildragger such as a 4-Star 40,60, etc. The snap or near-snap just after lift-off results from a tip stall condition because the pilot does not induce or maintain proper rudder control rather than simply using aileron.
The model is allowed to leave the earth too early with the tail still down. model is not really yet "flying". It is lifted off at a high angle of attack. It rolls left, the pilot quickly uses aileron -- rather than rudder -- to correct this. The left down-aileron completes the stall requirements for the left wing and so another nice model rolls over into the ground. the pilot has no clue to his problem, which is simply poor pilotage.
Had the pilot used rudder to maintain a straight flight out, plus maintaining a climb angle of not more than 10-12* he would not have had a bent-up machine.

Actually the same applies to landings. Use rudder coordination with the ailerons on approach. During the round-out phase try to stabilize the landing by maintaining slight rudder downwind and some aileron to hold the wing slightly down into the wind.
Definitely coordinate the rudder for any large aileron inputs. Rudder can prevent adverse yaw which is also a contributor to the tip-stall, be it takeoff or landing, or a high speed turn around a pylon.

Angle-of-attack (AOA) is the only factor that a pilot controls to make a wing stall. Everything else is simply prevention of exceeding critical AOA.

Edit; Typo