It means 'special' in Polish and it's a category of aircrafts in our regulations

@PeterPasieka The airplane lost type certificate in 2008, which means the manufacturer abandoned the design, and is no longer responsible for the airframe. The airplane is thus registered as specjalny, which means special in Polish. It's the same as "experimental" in the US. This is because the manufacturer will not release any more bulletins about the airframe, and it's the sole responsibility of the owner to keep it in good shape.