In the Harry Potter series created by J. K. Rowling, magic is depicted as a natural force that can be used to override the usual laws of nature . Many fictional magical creatures exist in the series, while ordinary creatures sometimes exhibit new magical properties in the novels' world (owls, for instance, have been trained to deliver post). Objects, too, can be enhanced or imbued with magical property. The small percentage of humans that are able to perform magic are referred to as witches and wizards, in contrast to the non-magical Muggles.
In humans, magic or the lack thereof is an inborn attribute. It is inherited, carried on "dominant resilient genes." Magic is the norm in the children of magical couples and less common in those of Muggles. Exceptions exist: those unable to do magic who are born to magical parents are known as Squibs, whereas a witch or wizard born to Muggle parents is known as a Muggle-born, or by the pejorative "Mudblood". While Muggle-borns are quite common, Squibs are extremely rare. For more, check this : http://en.wikipedia.org/wiki/Magic_in_Harry_Potter