In the Scripting Define Symbols field, you can add your own custom scripting #define directives to the built-in selection available. For each build target, enter the names of the symbols you want to define. You can then use these symbols as the conditions in #if directives, just like the built-in symbols. For more information, see [#define directives](https://docs.unity3d.com/Manual/PlatformDependentCompilation.html?_ga=2.140584053.690056806.1634230315–349158170.1626113345)
For more information, see Platform-dependent compilation.