I remember in a philosophy class during an in-class test we were supposed to cite a source from texts we had read in class, but were only able to bring a short list of the authors and pages that we wanted to cite for the exam

I remember in a philosophy class during an in-class test we were supposed to cite a source from texts we had read in class, but were only able to bring a short list of the authors and pages that we wanted to cite for the exam. We were told to use a specific in-text citation if we were unable to cite the exact page which basically meant "will provide source if asked". It was two letters I believe, something like (e.g.) or (a.d.)? I'm having a very hard time finding out what this is and I'd appreciate absolutely any help!