A predefined function in ABAP that can be used in certain operand positions. Available as numeric functions, string functions, table functions, and byte string functions. The return values have the corresponding data type. Description functions, which provide information about data objects, are also available. The names of the built-in functions are a subset of the reserved names. Built-in functions are also available in ABAP SQL and in the CDS DDL in ABAP CDS.