It has been called New Orleans jazz, Dixieland (a term that most of the musicians playing it despise), and most recently, “trad” (short for “traditional”) jazz. Ever since Benny Goodman exploded onto the pop-music scene in 1935 and ignited the swing era, the earlier jazz of the 1920s has been relegated to music’s margins.

But a funny thing happened on the way to the modern bandstand.

Gradually, over the past few years, more and more young jazz musicians—mainly in their 20s and even younger—have begun to play this music and, in the process, started again to refer to it by the name it was known by when it was new: Hot Jazz. Ninety years ago, dancers employed designations of temperature to distinguish between “hot” bands, like King Oliver’s Creole Jazz Band or Jelly Roll Morton’s Red Hot Peppers and the “sweet” bands of the era, like Guy Lombardo’s.

All of a sudden, Hot Jazz bands are all over New York (and, by various indications, other cities as well)—most of them made up of musicians roughly the age of trumpeter Mike Davis and Joshua Holcomb (who plays trombone, tuba, and bass), both 21. The two are recent graduates of the Manhattan School of Music, where they jointly led a Hot Jazz student-ensemble band, and are now part of the city’s workforce of professional musicians. Such bands are heard in an increasing number of clubs, including several devoted to Hot Jazz, such as Mona’s in the Alphabet City neighborhood, and Radegast Hall & Biergaretn in Williamsburg, Brooklyn.

Nearly every week (particularly in the summer), these musicians also play in bands at dance-oriented “retro nouveau” events, like Shanghai Mermaid, the Jazz Age Lawn Party, and the Salon—a combination of dance, concert, and costume party. Young dancers typically come in 1920s drag, and one can see flappers and sheikhs texting and tweeting on the margins of the dance floor.

The Lawn Party, the biggest of these events, usually attracts 3,000-plus people (most in vintage attire, almost all under 30) for two weekends a summer on Governors Island. Movie director Baz Luhrmann is a regular attendee, and although his film adaptation of The Great Gatsby—based on the definitive novel of what author F. Scott Fitzgerald called “the Jazz Age”—featured little authentic jazz from the period, the movie’s box-office success reveals again how the culture of the Roaring 20s seems to resonate with contemporary audiences.

Hot Jazz is so prevalent now that New York has almost become like New Orleans in the fin de siècle period: in covering the city’s jazz scene for The Wall Street Journal, I find that I can go hear a 20s-style band, almost inevitably made up of musicians born well after 1980, playing somewhere in the city virtually every night of the week. For these young players, the pot of gold at the end of the rainbow is Vince Giordano and the Nighthawks, the 11-piece ensemble that’s kept the torch burning for pre-swing music for almost 40 years. Most of Giordano’s regular musicians are in their 40s and 50s, but he occasionally hires up-and-coming artists, such as 26-year-old twins Peter and Will Anderson, two reed players (clarinet and saxophone) who have been working with Giordano since 2007, their sophomore year at Juilliard.