Historically, disinformation is an intelligence term meaning purposely giving false information. A classic example is the British leaking false information on the capabilities of the radar to German intelligence in World War II. This led to the battleship Bismarck inadvertently sailing within radar range, being located and sunk.
Successful disinformation must be plausible and must contain elements of truth mixed with apparently plausible lies. Disinformation is ubiquitous in today's media world. It is much easier to muddle the field by spreading plausible sounding but at least partly false stories than to keep absolute secrets.
Disinformation is not limited to politics or military matters. The organized religions may be the most successful and grand disinformation operations ever perpetrated on man. Again, this does not mean that all the precepts therein be false, rather it means that things which are as such valid have been used as a vehicle for planting a message that has justified war, bloodshed and misery throughout history. Also, much of the New Age appears to be geared at misleading people into practices that sound like good ideas but have quite the opposite effect. The "you create your own reality" meme is an example.
For example, the article "Who Wrote the Bible" at the Cassiopaea.org site deals with this aspect of disinformation.