TWYLA THARP doesn't care what you call "Movin' Out" -- musical, Broadway show or even the unappealing "dancical" (although she complains it sounds like a Popsicle and wonders what color it is). "Billy and I agreed in Chicago that we were calling it nothing. We call it its title," Tharp says. "It was everybody else's problem if they needed to have a box. . . . They'd have to do the naming." So "Movin' Out" it is. And Billy? He's Billy Joel, singer, songwriter and pop piano man, who gave choreographer and director Tharp the go-ahead to select from and assemble his songbook into a two-act narrative, sans dialogue, that unwinds through lyrics and choreography.

Opening Friday at the National Theatre for a four-week run, "Movin' Out" concerns the whirlwind coming-of-age of high school friends -- remember Joel's characters in "Scenes From an Italian Restaurant" and "Uptown Girl"? -- but ultimately it paints an expansive portrait of an American generation during the late 1960s and early 1970s. Brenda and Eddie don't make it beyond their high school sweetheart days, while James and Judy are ready for the altar. Tony, unattached, seeks a relationship. But everything changes when the men ship out to Vietnam and return changed to a nation that has lost its innocence. Twenty-four of Joel's songs accompany Tharp's dances.

Tharp, among the most prolific and widely known choreographers at work today, is known for her loose-limbed aesthetic that culls from ballet, modern, tap, jazz and social dance forms. She has traversed the lines that commonly separate dancers into camps. In a career that spans 40 years, she has choreographed more than 125 works, both for her own company and for American Ballet Theatre, the Paris Opera Ballet and the New York City Ballet, among others, as well as five Hollywood movies and two Broadway shows, which she also directed. "Movin' Out" has been playing on Broadway since October 2002. A MacArthur "genius" fellow, Tharp wrote "The Creative Habit," a primer on the nuts and bolts of creativity.

Tharp was raised in Southern California, where her father ran a drive-in movie theater. "Growing up I saw movies all the time without a soundtrack. So I saw stories being told without hearing the language." In her head Tharp played out her own narratives to these wordless moving pictures. "I'd like to think they were somewhat in the realm of what the filmmakers did. Essentially I learned to read story without the spoken word."

For Tharp, nonverbal narrative is a no-brainer, though outside the dance studio she often finds others wary of her wordless storytelling. "I think it's simply because people in theater attach content to language. Some also attach it to acting, but it's in the context of a script. And I think that the notion of a silent story is not something that comes rapidly to mind for people because it hasn't been done," she says, in mainstream venues, though ballet and non-Western cultures have centuries of history in dance narratives.

"Originally I did 'Movin' Out' because I felt that finally in our culture that we had come to a denouement in the split that the country suffered in the late '60s and '70s," she says. "The theme of 'Movin' Out,' " she explains, "is essentially return. In other words, Eddie, who's our main protagonist, is allowed to return and is allowed to be reabsorbed into his society and his world."

MOVIN' OUT -- Through Dec. 19 at National Theatre, 1321 Pennsylvania Ave. NW. 800-447-7400 or Telecharge.com.

David Gomez and Holly Cruikshank in "Movin' Out," choreographed by Twyla Tharp to songs by Billy Joel. The production opens this weekend.