The phrase "second day" refers to the second full day in a sequence. It is calculated by counting from the first day, which is usually considered as Day 1 or Sunday, and then adding one more day to it. For example, if an event happened on Tuesday, we would say that it occurred on the second day of the week because Monday was counted as the first day. In summary, "second day" means the second full day in a sequence following the first day or Sunday.