These terms represent different stages of progression.
A Provisional Judge is a non-BJCP person who has passed an online Entrance Exam. They are not a member of the BJCP, but are qualified to take a Judging Exam.
An Apprentice Judge is an active BJCP judge who has taken a Judging Exam, but not passed it. Apprentice is a time-limited BJCP rank to encourage the judge to pass the exam. An Apprentice judge is a member of the BJCP, but does not have full member privileges (e.g., cannot vote).
A Rank Pending judge is just that; a judge whose rank is pending. Rank Pending is not a BJCP rank; it is a term used on scoresheets to identify someone who has taken the exam but not yet received results.
An Affiliated judge is an Apprentice Judge who did not become a full member by passing a Judging Exam. Affiliated is a status, not a rank. It means that the person is no longer considered a BJCP member, but retains their ID in case they subsequently pass an Entrance Exam and the associated Judging Exam. An Affiliated judge should check the Non-BJCP checkbox on the scoresheet.