By default all active and enabled properties result in either one or two #define'd symbols in the package's configuration header file, and this is one of the main ways in which options can affect packages at build-time. It is possible to suppress the default #define's by specifying a no_define property in the body of an option or other CDL entity. This property takes no arguments and should occur only once in a given body.
The no_define property is frequently used in conjunction with one of the other header-file related properties such as define. If one of the other properties is used to export the required information to a configuration header file then often there is little point in exporting the default #define as well — in fact there could be a name clash. The no_define property can also be useful if the sole purpose of an option is to affect which files get built, and the default #define would never get tested in any source code. However in such cases the default #define is mostly harmless and there is little to be gained by suppressing it.