If the pretentious multilingual teaser that runs before each film at one local first-run art house is to be believed, “The language of cinema is universal.” But when it comes to American film genres, the language of cinema history is certainly not. The term “B-movie” has become a catchall buzzword describing any sleazy, low-budget, hastily prepared movie. With Quentin Tarantino and Robert Rodriguez’s exploitation picture valentine “Grindhouse” due in theaters momentarily, the term is now being used to describe an intentionally sleazy, high-budget, two-years-in-the-making movie. Starting today, Film Forum will present “B-Musicals” a 49-film, all-dancing, all-singing exercise in the true meaning of “B-Movie.”

In the halcyon days of old Hollywood, feature films were nearly always presented in double bills. The studios always shared profits with exhibitors on a percentage basis for the first feature, and at a flat rate for the second film. “A theater contracted for so many second features a year,” said Bruce Goldstein, film programmer at Film Forum, “so the studios had to mass produce them.”

Most of the majors directed their financial and creative energies into making the top-of-the-bill A picture as appealing as it could be. This left the smaller studios (and smaller production units within the bigs) with the job of filling out the B-film slot. A bottom of the bill B-movie was either a quickie from a prestige dream factory like Twentieth Century Fox or Paramount (and semi-bigs like Columbia, RKO and Universal), or a best effort from a poverty-row assembly line studio like Republic, Monogram or PRC.

When one thinks of the venerable tradition of the American musical movie, MGM and the famed Arthur Freed Unit, birth place of “Singin’ in the Rain,” “The Wizard of Oz,” and “Meet Me in St. Louis,” are more likely to come to mind than Western and serial factory Republic, or grade-Z PRC, the studio that made Edgar Ulmer’s squalid “Detour.” Nevertheless, throughout the 1930s, through World War II, and up until the Supreme Court forced Hollywood studios to divest themselves of their theater chains in the late ’40s, cheaply made musicals were a regular part of every B-movie production slate.

Yet these musicals are perhaps the least known genre relics of Hollywood’s golden age. Local reperatory screens and DVD and Turner Classic Movie showings have kept the A-musical at center stage for decades. “But the Freed unit’s been done to death,” Mr. Goldstein said. “I grew up in New York, which is old-movie central, and I don’t remember most of the films in this series ever even playing on TV. It was always Astaire and Rogers, but Donald O’Connor and Peggy Ryan? Never.”

Films like 1941’s “San Antonio Rose” and 1942’s “Strictly in the Groove” “haven’t been shown anywhere,” Eric Spilker, a B-movie obsessive and one of several contributing experts involved with Mr. Goldstein’s series, said. “They were offered for sale to television in the ’60s, but nobody bought them.” Shorn of their double-bill context, often barely an hour long, and fronted by decidedly non-marquee names, some of the most well-crafted oddball entertainments ever to come out of Hollywood have remained in half-remembered pop culture twilight for decades.

“A lot of these films just disappeared,” Mr. Goldstein said. “They’re not big enough to make it to DVD and most of them are not even on TCM. They’re impossible to see. But I was impressed by the couple that I’d managed to see over the years.”

Fortunately, many of the forgotten films in Film Forum’s series have only vanished from the screen, not from the vaults of the studios that made them and copyright holders and collectors that acquired them.

“Hollywood is finally getting its act together when it comes to their heritage,” Mr. Goldstein said. “Sony [which owns the Columbia Pictures catalog, among others], for instance, wants to make prints of everything they have.” Thanks to this relatively recent consciousness-raising in the formerly history-phobic corridors of corporate Hollywood, Mr. Goldstein was able to secure brand new 35 mm prints of films that no one has seen for decades.

On poverty row, lightning-fast schedules and threadbare production values were the order of the day. But viewed in hindsight, these clearly recognizable limitations have become an aesthetic. “When you watch the Columbia B-musicals, you realize that they’re made on the same cheesy sets as the Three Stooges films,” Mr. Goldstein said. “But the people who made these films knew how to do musical numbers, something which they seem to have forgotten today. They knew how to shoot orchestras. They knew how to shoot dancers and performances. No matter how mediocre the material, they knew how to do it.”

For instance, 1944’s “Carolina Blues,” starring Ann Miller and “College of Musical Knowledge” bandleader Kay Kyser, briskly builds to a show-stopping finale performed by one half of legendary movie dance team the Ritz Brothers (perhaps the producers couldn’t afford both). “It’s an amazing production number,” Mr. Goldstein said. “It’s as good as anything in an A-musical.”

Like the B-Westerns, costume dramas, and crime films with which they shared the assembly line, Bmusicals were a training ground for on-camera and behind-the-camera talent whose careers would outlast poverty row. “That’s something about them that’s amazing,” Mr. Goldstein said. “You’re watching a programmer like ‘Reveille With Beverly’ and all of a sudden you’ve got Duke Ellington and Frank Sinatra onscreen.”

1949’s “Ladies of the Chorus” features Marilyn Monroe in one of her first top-billed roles. Directed by Phil Karlson, who would bridge the gap between old-time B-movies and ’70s exploitation cinema as producer and director of the future drive-in classic “Walking Tall,” “Ladies of the Chorus” offers Monroe as the younger half of a mother-daughter burlesque team.

Mom is played by Adele Jergens, in real life barely nine years Monroe’s senior, and the film is blessed by a backstage bizarro-world plot that builds to a borderline surreal party sequence and a gently moralist twist. The film has the relentlessly forward motion of a confused but vivid dream. Yes, they don’t make them like this anymore. They couldn’t if they tried. But at Film Forum for the next month, it’s possible to relive a time when they made them like that by the score.

Through April 19 (209 W. Houston St., between Sixth Avenue and Varick Street, 212-727-8110).