There’s no such thing as KDE 5

Use of the KDE tricronym to refer to the desktop environment began to be phased out after version 4.5, which was released with another two letters, becoming KDE SC (Software Compilation). Nowadays, the KDE monicker tends to refer to the whole community centred around the desktop.

While the underlying Qt libraries have always been separate from the desktop environment that they power, KDE 4 gave rise to a number of auxiliary libraries (collectively lumped together and referred to as kdelibs), some of which were part of the desktop itself, and some of which were only required for certain applications.

In the latest incarnation of the desktop, these libraries have been updated and rearranged: some of their functionality is now provided by Qt components, some have been annexed into a collection referred to as KDE Frameworks (Kf5) and the rest are bundled with any applications that require them. The applications themselves constitute a suite called KDEApplications and the new desktop environment is known as KDE Plasma 5.

Decoupling the applications from the desktop enviornment is a bold move, but certainly is mutually beneficial: Plasma users are free to pick and choose which applications they want to install, and users of other desktops can install a KDE application without bringing most of the desktop with it. Likewise the compartmentalisation of Frameworks and Plasma allows LXQt to be what it is: a lightweight Qt5- based desktop that relies on a couple of Kf5 libraries whilst being entirely independent of the Plasma desktop.