Open carry means that all or part of the gun is plainly visible.
Basically, is it visible and obvious you are carrying a firearm that is not covered or concealed in any way (i.e., a standard belt holster with no clothing over the gun would be considered open carry; printing, flashing, etc. would still be considered concealed.)
In Kansas, open carry can be regulated by local municipalities, so to do so legally requires greater research on the area(s) you plan to open carry on. If you hold a concealed carry permit, then you can carry concealed anywhere in the state (unless prohibited by law). This does not extend to open carry - for example, Topeka and Witchita both ban the practice.
For a more visual example of the differences, here are some photos made by nikerret:
Concealed Carry (would be considered 'flashing' in this picture):
If you have a CCW permit, then you can carry in more places, openly or concealed. For example, the Gun-Free School Zones act restricts non-permit holders to carrying at a certain distance from public K-12 schools. You are also not required to place your firearm in a clearly visible location while in a vehicle - permit holders may carry concealed or openly within vehicles. Vehicles are something of a grey area if you do not have a permit, and I'd need to do more research there.
Note that all of the above pertains only to the state of Kansas - other state laws will vary. Also, I am not a lawyer, so the above information may be flawed/inaccurate/incorrect.