What is a "pre-trial (hearing)"?

A pretrial hearing, sometimes called a pretrial conference, is a meeting of the defense, the prosecution, and the judge before a trial commences. If one party does not appear, the judge can impose sanctions. During this hearing, a range of documents may be presented, evidence can be presented and excluded, and more. It occurs before the preliminary hearing, but many things can be done at this time, such as:

Attorneys can file a range of motions.
Which evidence can be presented and which cannot.
The judge can determine if there is fair cause for a trial.
Plaintiffs can enter plea agreements.
Note that the pretrial hearing does not revolve around guilt or innocence, but the hearing does bear directly on the outcome of your case. It is essential that you attend a pretrial hearing with an experienced criminal defense attorney to represent you.

It is a meeting to see if the case warrants a full-on trial.

Thank you both very much.
I learned some things today.

Pretty good answers above.

I’d only add that preliminary/pretrail hearings allow prosecutors to present evidence that may not be allowed later in a full trial, defendants may waive any rights they may have to appear, and in the US the hearing process & rules may vary in different jurisdictions.

Most episodes of Perry Mason are pretrial hearings.