Simple Definition:

Electric charge is a fundamental property of matter that causes it to attract [pull] or repel [push away] other objects that have electric charge. For example, when you rub a balloon on your hair, the balloon becomes charged and can stick to a wall because of the attraction between the charges on the balloon and the wall.

Very Simple Definition:

Electric charge is a special property of things that makes them either pull or push other things that have this property. For example, when you rub a balloon on your hair, the balloon becomes charged and can stick to a wall.