What are the key differences between a PhD candidate and someone who is ABD (All But Dissertation) in terms of their progress towards completing a doctoral degree?

The key difference between a PhD candidate and someone who is ABD (All But Dissertation) is that a PhD candidate has completed all the requirements for their doctoral degree, including coursework and exams, and is actively working on their dissertation. On the other hand, someone who is ABD has completed all requirements except for the dissertation, which is the final step towards earning the PhD.