what is the meaning of phd degree

Perhaps you may have seen someone express their student status in such a way, which may work informally depending on the context (perhaps a listing of students, which may have included undergrads and masters level students, and could thus differentiate). E.g.:
Is it correct to express PhD in brackets “(PhD)” as suffix to express the ongoing degree?

You must pass at least two exams, known respectively as the A and B Exams. Some fields require an additional qualifying examination known as the Q Exam.
Passing the A Exam means the graduate faculty believes that you are ready to proceed into the dissertation phase of your degree program.

References:

http://gradschool.cornell.edu/academic-progress/requirements-milestones/exams/exams-required-for-ph-d-degree/
http://www.thefreedictionary.com/PhD