A married print is one that has the soundtrack "attached" to the film, so it plays (as it should) in a projector.
When a film is in previews, and by that I mean they're showing it to audiences before it's entirely done to see if what they got is what they think they got, the soundtrack isn't yet married.
A gaggle of studio technicians will come into the theatre where you're working and install a special interlocked device to play the soundtrack in one projector at exactly the same rate as the film as it goes through another projector. (A drift of a mere frame per minute can turn into mis-syncing within 5 minutes. An audience can tell if the sound isn't coming out of the mouth the way it's supposed to.)
Back in the late '80s, the Samuel Goldwyn company came into the theatre I worked at to test-screen the new Lauren Hutton vampire comedy, "Once Bitten" (which also starred Jim Carrey, before he would explode into stardom with "Ace Ventura"a year later). They were worried (they weren't sure how the film was really going to play, in its rough state) and had 2 unannounced screenings, a couple months before it was released, one at 6:00 and one 9:00. They recruited a young crowd for the 6:00, telling them only that it was a "comedy" from a major motion picture company, and they found out what they already knew: that the film wasn't working.
It was a rough cut, admittedly, and some of the sound wasn't finished and transitions weren't very elegant. It was a work print, and the actual splices were still in this copy. (They expressed concern that they had all be checked to make sure they didn't break during projection. It would wreak havoc ("Reek"? "Wreck"?) with the sound syncing playback.)
They ran a hand-held sound mixer with a wire back to the booth to the middle of the auditorium, and a sound guy sat there through the film adjusting levels depending on the way the mix sounded in the crowded auditorium.
The film ran over 2 hours. There was one sequence in particular that stopped the film dead, about 40 minutes in. It was some talky scene in which someone (not Mr. Carrey) talks about their motivation or backstory with someone else, and from that point on nothing seemed to work until the end. It was as if the scene sucked all enthusiasm or ability to laugh out of the audience.
It had to go.
After the first show was over and the audience response cards were read, the technicians in the booth found the spot in the film, in reel 3 and held the film up to the light. They then took a scissors and cut the film and dumped it into the garbage can.
A hundreds of feet of the stuff. About 5 or 6 minutes of film. It was amazing. And across the booth, another pair of technicians dumped the corresponding soundtrack-ed reel sequence into another trashcan.
It was the epitome of high-level crunch-decision Hollywood editing at its finest.
The 9:00 show went much better. Later, as they were packing up, I asked if they intended to keep the deleted scene they had in the trashcans.
They said they were taking it with them, to burn.
