In the 16 personalities, MBTI, and Socionics Models, the letters P and J should not be explained in a practical way. Their definitions are within the model and can’t be explained outside it. This leads to opposite definitions and ends up confusing each I**J with each I**P with the same middle letters. Like INFJ with INFP and ISTP with ISTJ. The common explanations of P and J are only valid for extroverts, the ones with E***.
For introverts, it’s actually the opposite in practice.