Final answer:
The keyword for using default getters and setters in Objective-C is 'synthesize', but its usage is optional due to automatic synthesis provided by the compiler in recent versions of the language.
Step-by-step explanation:
The keyword used when a developer wants to use the default getters and setters in Objective-C is synthesize. However, as of more recent versions of the language, the use of synthesize is optional due to an automatic synthesis feature that the compiler provides.
If you do not declare either synthesize or dynamic for your property, Objective-C will automatically synthesize it with an underscore-prefixed ivar. This automatic synthesis is often sufficient, meaning that developers do not necessarily have to specify synthesize anymore unless they need to customize the backing variable's name or synthesize manually.