ASN.1 is the language for structured information describtion. That is why, it is typically used for information that has to be conveyed acros some interfaces or communication medium. It is internationally standardised by CCITT (ITU-T) standard X.409. The name (ASN.1) comes from ISO later.
The big effort of ASN.1 is that any ASN.1 message can be mechanicaly derived by aplying a set of rules, ones of them - Basic Encoding Rules - are standardised.