There are these positions in the Polish academic system:   In some institutions there is a position called 'docent', which corresponds roughly to 'adiunkt z habilitacją' and/or 'profesor nadzwyczajny' with 'habilitacja' but without the third doctorate called 'praca profesorska'.  Roughly, 'asystent' corresponds to nothing in the US system, 'adiunkt' and 'adiunkt z habilitacją' correspond to Assistant Professor in the US system, while 'profesor nadzwyczajny' without the third doctorate corresponds to Associate Professor and 'profesor zwyczajny' corresponds to Full Professor in the US system. Needless to say, the correspondences in question are very rough indeed.
 Another intricacy—which seldom fails to baffle and confuse a foreigner and sometimes even a native—is what all these things are labelled as.

Thus, Master or 'magister' is not labelled at all, Phil. Doc. or 'doktor' as well as Phil. Doc. with the second doctorate, 'habilitacja', are labelled academic degrees.  The third doctorate, finally, 'praca profesorska', is labelled a title—nay, the titlethat of 'profesor', there being only one academic title in Poland. This title, strangely enough, does not entitle you to anything (except calling yourself 'profesor tytularny'—Poles, in general, are rather fond of titles and distinctions, hierarchies and other bells and whistles) and in particular it does not guarantee you a university position, although it certainly goes a long way towards obtaining one.  It is somewhat similar, but not directly comparable to 'Higher Doctorate'  a rare distinction sometimes awarded in some Anglo-Saxon countries.
So, 'profesor' is an ambiguous term in Poland: it can either signify an academic position or the academic title which its bearer is entitled to even if he does not hold an academic position. Besides, all grammar school teachers were traditionally called professors, and some non-university teachers are so called even today. 

The Polish system is modelled on the (former) German and partially Soviet systems: in both of them, a necessary condition of obtaining the position of professor is a second doctorate (Habilitation in Germany), unknown in the Anglo-Saxon world, France (until recently), Italy, the Netherlands or the Scandinavian countries. The catch is that in Poland you have to obtain a third doctorate (called 'tytuł profesorski') to apply for a full professorship, and the second doctorate (called 'habilitacja') is just an additional hurdle. On the other hand, Poles are generally fond of  degrees and distinctions, so climbing up this Byzantine hierarchy is to many of them a matter of pride and pleasure.

To the American degree of  Bachelor there corresponds in Poland something that is neither called nor labelled as anything at all, but the status of someone who has reached this nameless distinction is called 'licencjat'.

Now you are duly intimidated, we hope
—and rightly so, because it is anything but easy to be a 'profesor' in Poland, however many doctorates you might have written or failed to write.
There are many other weird things in the Polish academe and outside of it, most of which are due to the vicissitudes of Poland's recent history, such as not being a state at all between 1795 and 1918 (partitions of Poland), being a satellite state of the Soviet Union between 1944 and 1989, and many others. It is to be hoped that one day we shall settle down and 'return to normalcy', as President Harding would have put it. (If you want to understand the history of Poland a good starting point is The Polish Way by Adam Zamoyski.)