What is a preview?
Pre - indicating that it is before something rather than pro which would indicate after some action or event. I.E. Preceeding the concert we got something to eat which shows that before the concert some action was taken.
Preview can be applied in a variety of ways. Previewing a movie for example may indicate that you watch a clip of a motion picture before you decide on going to see that movie or not.
It can, in its own way indicate that something may be viewed by an invited audience to be viewed before it is open to the general public for viewing. In other words, you have previewed it before others have had the chance.