A summary judgment is basically a ruling by a judge saying that one side in a civil case would be absolutely certain to win the case and therefore there is no need to bring the case to trial. The case is then resolved in favor of the party that has made the motion for a summary judgment.
There have to be two things that are true in order for summary judgment to be granted. First, there have to be no real issues of fact that are left to be disputed. In other words, both sides have to agree on what all the relevant facts in the case are. Second, the law must clearly be in favor of the party that is moving for the summary judgment. What this means is that the court would certainly rule for the party after applying the relevant law to the facts that have been agreed upon.
By granting a summary judgment, a judge allows the parties to avoid the expense and difficulties of a trial.