In computer science, the abstract syntax of data is its structure described as a data type (possibly, but not necessarily, an abstract data type), independent of any particular representation or encoding. This is particularly used in the representation of text in computer languages, which are generally stored in a tree structure as an abstract syntax tree.

<language, data> A representation of data (typically either a message passing over a communications link or a program being compiled) which is independent of machine-oriented structures and encodings and also of the physical representation of the data (called "concrete syntax" in the case of compilation or "transfer syntax" in communications). A compiler's internal representation of a program will typically be specified by an abstract syntax in terms of categories such as "statement", "expression" and "identifier". This is independent of the source syntax (concrete syntax) of the language being compiled (though it will often be very similar). A parse tree is similar to an abstract syntax tree but it will typically also contain features such as parentheses which are syntactically significant but which are implicit in the structure of the abstract syntax tree. (1998-05-26)

<compiler> (AST) A data structure representing something which has been parsed, often used as a compiler or interpreter's internal representation of a program while it is being optimised and from which code generation is performed. The range of all possible such structures is described by the abstract syntax. (1994-11-08)