Well, more appropriately, it isn't when the wing's lift doesn't exceed the weight, certainly a controlled descent is one where the lift is less than weight, etc.

The stall happens when the wing reaches an angle of attack, usually along with a slower airspeed, at which the flow over the wing separates, resulting in the wing no longer producing the lift it was. There is still lift being generated but it is significantly less. The speed at which this occurs is usually low but is a function of the angle of attack that the airplane is flying at.

The typical sport airplane will stall, pitch forward with some altitude loss and as the speed increases the flow will reattach and it will start flying again.

There are special cases like the modern 3D airplane that takes advantage of the wing's ability to produce lift in the fully stalled condition. They fly many maneuvers based on this along with some thrust help.

The big problem that can happen with a stall is when it is asymmetrial and rolls the airplane into a spin. Especially bad when you are about 10 feet lower than the altitude needed to recover. It makes it prudent to have fairly small control inputs when doing a landing approach to not force the airplane into the stall.

Practice doing stalls at altitude in order to know when they might happen and to avoid those flight conditions.