What does it mean when a show or soap opera is pre-empted?

Guding light, as the world turns, passions, etc.

What does it mean when a show or soap opera is pre-empted?theater seating

It means that another show has been put on in its place generally as a one time occurance.

What does it mean when a show or soap opera is pre-empted?lyric opera opera theater

Something more interesting to the masses is aired instead.
The scheduled programme isn't on, usually because of some sporting event. It will be rescheduled to be shown at another time, usually the next day.