I believe many people think the term "Maaseh Rav" means a story of a Rabbi: since we see from the story that a Rabbi acted a certain way, we can bring this as a proof to the halacha. However, I believe another understanding of the term is "Maaseh, Rav" meaning "A story is greater": that if one can bring a story of how a Rabbi acted in a particular case then that will be greater in determining what the halacha is (greater, that is, then other proofs that could potentially be brought perhaps in terms of savarah, earlier sources, etc.). While I think both understandings practically mean the same thing, I believe the second better reflects what the phrase really means (when being used in the gemorah). However, I don't have a proof for this. Can someone please cite a source or example, or give any more insights into this?
Maaseh Rav is translated differently by three dictionaries:
The term appears in several places in the Talmud, including Shabbos 21a and 126b, Baba Kama 68a, Baba Basra 130b and Nidda 65b.
Translating Maaseh Rav as "A story of a sage" does not make sense in this context.