A short circuit in an electrical circuit

Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...

 that allows a current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 to travel along an unintended path, often where essentially no (or a very low) electrical impedance

Electrical impedance

Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

 is encountered.
The electrical opposite of a short circuit is an "open circuit

Open-circuit voltage

Open-circuit voltage is the difference of electrical potential between two terminals of a device when there is no external load connected, i.e. the circuit is broken or open. Under these conditions there is no external electric current between the terminals, even though there may be current...

", which is an infinite resistance between two nodes. It is common to misuse "short circuit" to describe any electrical malfunction, regardless of the actual problem.
A short circuit is an abnormal low-resistance

Electrical resistance

The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 connection between two nodes of an electrical circuit that are meant to be at different voltages.