PCB stands for "printed circuit board". A PCB is a physical thing. It is a thin (2mm) rigid board of some non-conductive material, often with holes in it. On the board, there are "tracks" of a conductive material (usually copper). Electronic devices are soldered to the board, to create, in the real world, the circuit that you designed in the computer using KiCad.
A PCB is the ultimate goal of KiCad. In the KiCad documentation, we sometimes see "PCB" where what is meant the design for a PCB, but the context will usually tell you which is meant.
When I say "PCB". I may be referring to
*the screen of "stuff" that you see when working with KiCad's PCBnew module
*the physical object that you are setting out to make
*the design of lines, pads, holes, etc, which will be on the physical device. (The artwork)
I have tried not to be ambiguous, but it is hard! Do write and complain about any instance of ambiguity which was a nuisance for you. Please cite the page it is on, e.g. if it were on this page (surely not!), you would say "co1pcb". The first thing on every page (I hope! If not… write and complain!) is it's reference ID.
Here's a very simple example of a PCB design. I sometimes say "PCB layout", or "pcb artwrok" when trying to be clear that I am talking about the pattern of lines, etc. (Note: "layout" used as a noun there, not a verb.) Part of the reason references to "PCB" are ambiguous is that the finished, physical board would look much like this:
(I've tweaked the colors slightly, to make that more attractive.)
The good news is that often it doesn't matter if you are thinking "the actual board" when I am meaning, say, the artwork you see on your computer screen.
I have a FAQ answer on "How does a hobbyist make a PCB" for you. It discusses making your own boards. There's also a FAQ answer on "How to get boards made for you by commercial services."
The first one may be of general interest if you have no idea of the general principles of PCB fabrication. The name, "printed circuit board", is actually quite misleading.