Konsole is a X terminal emulation for the K Desktop Environment.
In the context of a graphical user interface being a terminal emulation means, that it's task is to provide a display to an application that is originally designed to run on a computer with a character terminal attached.
To give a short taxonomy of free X terminals, there' two other of this kind: xterm, which is the original, written even before X itself (a month or two), and xvt, a light-wight xterm clone, on which most other currently available derivates (notably eterm) base. After a decade, konsole is the first rewrite from ground up. While xterm has definitely been hacked to death meanwhile (it's README starts with the words "Abandon All Hope, Ye Who Enter Here"), konsole offers a fresh start using contemporary technologies and understanding of X.