A short circuit is the state in which current flows back to its potential source directly. It happens sometimes when the power supply lines contact each other directly. Also, conducting materials of a very low or negligible resistance in parallel to the potential source can cause short circuit too. A circuit diagram below this post helps to illustrate the meaning of short circuit.
In electronic circuits, short circuit mostly happens when the power component(s) for example; shunt resistors, power capacitors or filter capacitors, power transistors etc are faulty.
A short circuit is a faulty circuit which can result to fire in powerful circuits. To avoid fire or burning, connect protective devices in series to the power supply line of the circuit. The protective device can be a circuit breaker or fuse with correct rating.
The below circuit diagram illustrates the meaning of the term short circuit. See the circle which gives the emphasis of the short circuit.