It is normal to see house lights briefly dim or occasionally flicker during stormy weather or when a power-hungry appliance is turned on. Persistent or more pronounced problems with residential lights can indicate a serious problem and should be looked at by a trained electrician. Problems should not be ignored because faulty wiring can lead to fires.
If a single light fixture is the source of the flickering, the problem can be as simple as a loose light bulb. Check to ensure the bulb has been tightly screwed into the socket. If the bulb is securely in the socket and the problem continues, it could be a loose filament in the bulb. Replace the bulb and the problem should disappear.
If a single light fixture is still flickering after the bulb has been replaced, it could be a loose connection in the room's light switch. It could also mean the wrong type of dimmer switch is being used if the lights are fluorescent or low voltage. These types of lights need a specially rated dimmer in order to work properly. Check with your local hardware store for the appropriate switch.
The term "arcing" is used to describe electrical currents that jump from one wire to another. This happens when wire connections are very close but not quite touching. The amount of head produced by arcing varies, depending on the width of the gap and how much current is crossing the gap. Arcing usually doesn't trip the circuit breaker so power continues to flow. Acing can start a fire and if it is suspected, call an electrician right away.
Newer houses tend to have all their lights connected to a couple of circuits. This means a loose or unconnected wire in one of the circuits can cause multiple lights to flicker. Try turning off a circuit and checking which lights are connected to it. If the same group of lights are flickering, there's a good chance there's a problem with that circuit. An electrician should be called.