As a General Legal Borderline for Mitzvot/Transgressions involving amounts of food: Yuma 80a, Eruvin 4b; Succah 5b-6a; Pesachim 49b-50a
As the legal minimum of a prohibited item one ingests, to require a Sin Offering: Yuma 80a
Only considering an Olive eaten within the time to eat a "Peras" to be like eating an Olive, Biblically or Rabbinically: Pesachim 44a, 114b
Applying the above-stated rule to Mixtures containing Leaven: Pesachim 44a
The Olive-Size is determined by a Medium-Sized Olive: Yuma 80a
Swallowing an Olive in a big gulp: Pesachim 44a, 115b
A person's eating must match the norm: Pesachim 44a
Power of Human Courts to change the definition of an "Olive-sized amount": Yuma 80a
An Olive, liquefied, produces a "Reviit" Amount: Shabbat 77a