More commonly abreviated as ASN or ASN.1 (Abstract Syntax Notation One). It's the inter-national standard for representing and organizing data types and structures and arbitrary data sets.
The CCITT published the first original version of the standard as X.409 in 1984 after four years of collaborative work, and later a newer version resulting from a cooperative partnership of the ISO and CCITT, specified in X.208, apporved in 1988.
The latest, most common usage of the ASN system is in Secure Certificates utilizing the X.509 standard.