East Coast Swing, most commonly known in its simplified 6-count triple step form, is not a street dance - it is a ballroom studio adaptation, derived from various street swing dancing patterns and styles (especially LINDY HOP) at the height of the Swing Era.  The American Society of Dance Teachers, a group of independent instructors (many of whom were former Arthur Murray teachers) debuted the Jitterbug aka Lindy aka American Swing syllabus in 1942.  East Coast Swing is its most modern name, appearing on the scene decades later than the dance itself, as it was being taught to movie dancers quite a bit before 1942.  Since its inception, this ballroom-style dance been variously called, by ballroom studios: Eastern Swing, American Swing, Lindy, Jitterbug, and Western Swing.  And in various quarters, ALL those names are still used today to refer to the same. (The modern related ballroom style, INTERNATIONAL JIVE, is a British Ballroom Studio creation.).