The KDE Software Compilation (KDE SC) was an umbrella term for the desktop environment plus a range of included applications produced by KDE. From its 1.0 release in July 1998 until the release of version 4.4 in February 2010, the Software Compilation was simply known as KDE, which stood for K Desktop Environment until the rebrand.
The then called KDE SC was used for all releases from 4.4 onward until the final release 4.14 in July 2014. It consisted of the KDE Plasma 4 desktop and those KDE applications, whose development teams chose to follow the Software Compilation’s release schedule. After that, the KDE SC was split into three separate product entities: KDE Plasma, KDE Frameworks and KDE Applications, each with their own independent release schedules.