When a person hears "trial" they often picture movies with jurors sitting, listening to evidence, and determining guilt or innocence. Even outside of fictional television series, the jury trial often makes for popular viewing in such cases as the OJ Simpson and Casey Anthony trials. However, a trial can be held without a jury.
This is referred to as a bench trial, most often civil cases, or non-jury trials in criminal cases. In criminal cases, non-jury trials are generally the exception to the rule. Because criminal charges often have the potential for incarceration and conviction, a jury trial is the norm. However, for some very minor charges the State and defense may agree to have a non-jury trial rather than a jury trial. In addition, all juvenile criminal charges are tried in a non-jury trial, regardless of the severity of the charge.
So how is it a trial if there is no jury? In non-jury trials, the judge plays the role of the jury. Opening statements, testimony, evidence, and closing arguments are all reviewed and heard by the judge. The judge then acts as a jury would and determine if the State has proved the charge beyond a reasonable doubt. This creates a unique situation where a judge may also hear evidence that would normally be excluded from a jury; the judge is supposed to disregard this evidence or testimony, however.