A Software Development Kit (SDK) is a set of tools provided by the manufacturer of (usually) a hardware platform, operating system (OS), or programming language. SDKs help software developers create applications for that specific platform, system, or programming language. Think of it kind of like a toolkit, or the plastic bag of tools that comes packaged with the parts of a dresser you’ve bought to assemble yourself—only for app development. You have the building blocks—or development tools—you need to get the job done, and what’s included in the kit varies from manufacturer to manufacturer.
Typically, a basic SDK will include a compiler, debugger, and application programming interfaces (API’s).