A short circuit refers to a path with a very low resistance along which current can pass. Short circuits are usually created as a result of failure in insulation or when a substance that conducts electricity is accidentally dropped on a circuit allowing current to flow through it instead of following the normal path of the circuit.
The conducting path resulting in a short circuit has a very low resistance. This results in a large current flowing through the cell. As the flow of current creates heat, the cell is heated up. This may further lead to the formation of compounds that are highly volatility and not created in the normal operation of the cell. The net result of this is the cell getting damaged. In addition to the damage caused to the cell, a short circuit can also lead to the escape of dangerous compounds or create fires.
This makes it essential to ensure that short circuits are not created and electrical components such as circuit breakers are used to prevent damage even if a short circuit is created.