A "short circuit" is an unwanted connection of very low resistance such as a wire (almost 0) which provides a very easy path for current. Think of it as an electrical short-cut. It is normally used to describe a fault or accidental connection rather than a deliberate one.
For example: if the leads from a battery touch one another they create a very low resistance connection across the battery, so we say they have caused a short circuit across the battery. Current will flow through this short circuit rather than through the proper circuit. This stops the circuit working and it may cause a fire because the leads and battery will become hot with a large current flowing.
2
What is a schematic?
It is another name for a circuit diagram.
3
What does "open circuit" mean?
"Open circuit" means no connection. It is usually used to describe a break in some part of a circuit which could be deliberate (such as a switch in the open or off position) or a fault (such as a broken wire or burnt out component).
