English: "Year by year" — A teaching of the school of Rav: "year by year"—one day in this year and one day in that year; this teaches that a firstborn may be eaten for two days and one night.
On the daf / in context: When a firstborn is slaughtered at the end of its year, the consumption period extends into the following calendar day.
Type of Learning
Derash on the verse (Bekhoros) — a firstborn may be eaten for two days and one night.
What Is Learned
A firstborn animal that is slaughtered at the end of its year may be eaten for two days and the intervening night.