Truthfully they do not really indicate any degree at all. Progress toward completing a doctoral degree is typically divided into four stages. 1. Admission and qualifying exams if any 2. Coursework (not altogether unlike previous course work) 3. Preliminary examination to determine that candidate is ready to embark on independent research and 4 independent research ...i.e. the dissertation.
If you complete stage 3 of the above, you have done ALL BUT DISSERTATION. Hence the abbreviation A.B.D. It has no official standing anywhere.
Some doctoral programs that decide to let a candidate out after stage 3 may grant a master's degree as a kind of consolation prize. Others do not.
Hence the alternate explanation of the abbreviation:
ALL BUT DEAD.
Much luck to you in your completion of all 4 stages.