Answer:
It means that all requirements except for the dissertation have been completed. ABD = All But Dissertation.
This is an informal expression, and does not convey any official qualifications. In general, students still actively engaged in a PhD program who have passed all their qualifying exams are referred to as doctoral candidates. Thus, this expression is mostly used by people who are no longer actively engaged in their program. A dissertation is the essential component of a PhD, and those who do not complete one are generally competent at the masters level in their field.