Pesachim 2 - 8
The first mishna of our new mesechta states that the mitzvah to check for chametz before Pesach is “ohr” of the 14th of Nissan. What does “ohr” mean in this context?
Usually it means “light”, which would seem to imply that the mitzvah is the check on the morning of the 14th, the morning before the Seder. However, our gemara explains that according to all opinions — Rav Yehuda and Rav Huna — it means the night that begins the 14th of Nissan, a full 24 hours before the Seder.
The gemara explains that Tana of our mishna said “ohr” as a euphemism to express “night”. The commentaries explain that calling “night” as “light” is not a falsehood, G-d forbid, but teaches that the mitzvah of checking for chametz should be done at the very begin beginning of the night, at the transition between the last rays of light into darkness.
- Pesachim 3a
“Rav Yehuda said that Rav said in the name of Rabbi Meir that a person should always teach his student in a concise manner.”
- Pesachim 3b