Abstract Syntax Description Language appears to be part of the Zephyr project at the University of Virginia (and other places).

From their page:

• ASDL is designed to describe the tree-like data structures in compilers. Its main goal is to provide interoperability for compiler parts written in different languages.

http://www.cs.virginia.edu/zephyr/asdl.html

-- MikeVanEmmerik - 26 Feb 2002