SDK stands for software development kit and it is all about giving programmers the right tools for them to build applications for specific platforms.
The software development kit is made of programming tools, documentation to help programmers work and APIs. APIs are application program interfaces and are essentially a set of routines, protocols and tools used to build software applications.
There are different SDKs in the market today, some containing Java language, other containing Swift, .NET and so on.
Usually, SDKs are made available by companies and projects based on open source.
By using open source, companies bring in the expertise and different ideas from a wider sample of programmers instead of a small in-house team.
SDKs usually have at their core an integrated development environment (IDE), which turns out to be the central programming interface for the application-to-be.
Examples of SDKs include Apple’s Mac OS X SDK, iPhone SDK, or Microsoft’s Windows 7 SDK.