A program unit that is discrete and identifiable with respect to compiling, combining with other units, and loading, e.g., the input to, or output from, an assembler, compiler, linkage editor, or executive routine.

• 一种独立且可以标识的程序单元，可以单独编译，可与其它程序单元组合并装入计算机内存之中。如，汇编程序、编译程序、连接编辑程序或执行例行程序的输入或输出。