This is the 4854th most frequent Polish word.
osobistego
"Osobistego" means "personal" or "of personal" in English.
Here, "osobistego" is an adjective describing the car as personal, belonging specifically to the person speaking.
Nie mogę pożyczyć ci mojego osobistego samochodu.
I cannot lend you my personal car.
In this instance, "osobistym" (a form of "osobisty") pertains to privacy or intimacy in the context of information.
Ważne jest, aby chronić informacje o charakterze osobistym.
It is important to protect information of a personal nature.
Here, "osobistego" is an adjective describing 'development' as personal development, referring to individual improvement or progress.