A Roadshow Theatrical Release was once the prestige release format for the biggest Hollywood movies, especially for an Epic Movie.
What separated them from a regular or limited release was that they usually opened in a few select theatres and tickets were sold strictly on a reserved seating basis for a premium price and always in advance, often with stereo sound and Widescreen. The films' length was typically longer than usual with an Intermission in the runtime (and with an additional music-only "overture" before and "exit music" after the film) with typically no Short Film or Trailers on the schedule, which was usually just twice a day for Wednesdays, Saturdays and Sundays and just one a day for the rest of the week. Furthermore, people attending would usually receive a program for the film, just like a regular stage show.
Unlike today's limited releases, there was no question that a film getting such treatment would later be released wide, even the flops. However, they would often be recut for a shorter length for that release. As you might expect, this format was an expensive proposition that could be really embarrassing if the film turned out to be a turkey like Doctor Dolittle, but it could pay off with classic big films like The Ten Commandments and Ben-Hur, which could run for more than a year in that format.
This format had its heyday from The '50s to The '70s as the Hollywood studios desperately tried to draw audiences from their TVs to the cinemas. However, a series of flops in the 1970s finally killed interest in the format while stereo sound and widescreen became standard equipment in even the cheapest theatres. Today, when an epic movie is shown like Titanic (1997), it is on a general release with no intermission.
In other words, this format was the movie theater equivalent of the home video Limited Special Collector's Ultimate Edition.