Most people agree that a spoiled child is self-centred and demanding, inconsiderate of others and unpleasant to be around. The classic spoiled child sees himself and his needs as more important than anything else and does everything he can to get what he wants.
Sometimes adults think children who do unpleasant or annoying things are spoiled. But what adults see as bad behaviour may simply be normal behaviour for a child at that particular age and developmental stage. For example, it is not unusual for a 2-year-old who can't have something she badly wants to throw a tantrum. This is unpleasant and irritating, but it does not mean the child is spoiled.