Konsole and xterm are basically two different programs that do the same thing (give you a bash shell). Kinda like how Internet Explorer and Firefox are both web browsers. Each has different options/features/etc that some people prefer. When people are talking to you about terminal, they're generally talking about a command prompt, whether it is xterm, eterm, aterm, or konsole.
Desktop Environment and Window manager are different things. A window manager is the specific program that manipulates windows and allows you to have gui programs. It lets you resize boxes and move around each window. (I'm sure it's really more complicated than that, but stick with me.
) I believe KDE's window manager is called kwin.
Desktop Environments are the whole kitchen sink and include other programs that allow you to have icons on the desktop, a task bar, applets for network interfaces, etc. Fluxbox is just a window manager, but you can add on other programs like rox-filer to allow desktop icons, taskbars, etc and make it act like a Desktop.
I wouldn't be surprised if you hunted through the config files, you might even be able to make KDE use fluxbox as it's default window manager, but I might be wrong since there's so much integration of programs on a Desktop environment.