Many homeowners attempt to save money by doing minor repairs and upkeep themselves. Often times this could be dangerous, such as when those without the proper experience or know-how try to fix electrical wiring. It can be particularly dangerous coming into contact with an open hot wire.
An open wire, in the sense of wiring in a home, is one that is not connected to a circuit. When a circuit is closed, electricity flows through it and when that circuit is open, no power flows.
A hot wire is a wire that is active, live and receiving power. More often than not, the coating on hot wires is white.
When a wire is open and hot, that could mean it's come loose from its circuit. This is commonly seen in situations where outlets aren't giving out power, as the connections have come loose.
There are a variety of tools that allow you to test circuits for connectivity. These meters are touched to a wire; they send electrical impulses out to determine whether the wire is connected to a circuit or if it's open.
Leaving an open hot wire could cause problems in your wiring system. Beyond that, though, if a wire is not supposed to be open and hot, there is a risk that it could start an electrical fire.