Paranoia is a thought process characterized by excessive anxiety or fear, often to the point of irrationality and delusion. Paranoid thinking typically includes persecutory beliefs concerning a perceived threat towards oneself. In the original Greek, παράνοια (paranoia) simply means madness (para = outside; nous = mind). Historically, this characterization was used to describe any delusional state.
Sometimes in common usage, the term paranoia is misused to describe a phobia. For example, a person may not want to fly out of fear the plane may crash. This does not in itself indicate paranoia, but rather a phobia. The lack of blame in this case usually points to the latter. An example of paranoia, however, would be fear that terrorists are hijacking a particular plane to crash it, with no evidence to suggest such.
To save the trouble of Ancorp reading it in every post: Inokatsu