An electrical surge is a brief spike in voltage. They can be generated outside your premises or within it, depending on what equipment is malfunctioning (mainly electric motors, such as water pumps, building elevators, etc.). These surges can cause damage to electronic equipment within your home or office.
External power surges are typically caused by the restoration of power after an outage or blackout, aside from lightning strikes on the power grid. When there are internal power surges, there can be many causes, ranging from poor wiring to using too many extension cords and daisy-chaining power strips.
You can take precautions when designing a new home to prevent them, such as ensuring air conditioners and central heating do not share the same power lines as your appliance sockets. If your property is old, or if you rent, rewiring a whole house or office is often neither easy nor practical. When you're on the road or at someone else's home or office, it's the same. Wherever you are you can keep your electronics protected against power surges by using a surge protector.