The Mac developer program is a paid program that anyone who wants to develop and distribute Mac Apps can sign up for on the Apple website. For a nominal annual fee, membership in the program entitles us to a variety of services provided directly by Apple Inc. that are designed to help us develop and distribute Mac Apps.
Note
The Mac developer program is not the same as the iOS developer program. Developers who want to develop Apps for Apple's mobile platform need to sign up for the iOS developer program. If we want to develop and distribute software for both the Mac and iOS then we would need to sign up for both developer programs.