I believe ASL stands for American Semi Longbow(which is essentially what Mark said, an American style longbow). Most people today recognize it or refer to them as a Hill Style Longbow(fg backed and faced). It developed from Howard's pre fibre glass design, usually backed with boo, slight stringfollow. John Schulz, RIP used to specialize in these bows, deep handle, longer fades than the usual 2" fades that most people use these days, and narrow limbs rather than wide.
Miller Longbows (taught by Schulz) still make this style of bow, really nice-looking classic style of bow.