A macro definition is a set of statements that defines the name, the format, and the conditions for generating a sequence of assembler language statements. The macro definition can then be called by a macro instruction to process the statements. See topic Macro instruction for a description of the macro instruction. To define a macro you must:

• Give it a name
• Declare any parameters to be used
• Write the statements it contains
• Establish its boundaries with a macro definition header statement (MACRO) and a macro definition trailer statement (MEND)