A dispositive motion is a motion that requests that a judge throw out a case, or portions of a case before the case ever gets to trial.
Attorneys often make dispositive motions if they feel that the opposing side does not have a solid case. The judge decides whether or not the motion is approved.
There are a number of different types of dispositive motions. For example, motions for summary judgments, motions to dismiss, and motions for judgments on the pleadings are all different types of dispositive motions. All of these dispositive motions are designed to attempt to stop the trial from happening, or to get certain aspects of the case dismissed.
If a dispositive motion such as a motion to dismiss is approved by the judge, then the case can be thrown out.