The fourteenth day of Iyar is known as Pesah Sheni, or the Second Passover. On this day during the Temple period, there was an additional opportunity to bring the paschal offering, for those who were unable to bring the offering on the proper date (the fourteenth of Nisan) because they were ritually impure on that day or situated too far from the Temple. Such individuals would bring their offering on the fourteenth of Iyar instead, and eat matza with it. It was not necessary for them to remove all hametz from their homes even though they were bringing the paschal offering.

Today, although offerings are no longer sacrificed, there are still some customs that are observed in recognition of the special status of the Second Passover:

In the prayers of this day, Tahanun (a prayer of supplication omitted on festive occasions) is not recited. Some have the custom of not saying Tahanun already in the afternoon prayer preceding the Second Passover (the thirteenth of Iyar), as on every other eve of a festival.

Some people eat matza on the Second Passover, to commemorate the paschal offering that was eaten with matza. Some eat it on the night before the fourteenth, while others do so during the day, but the most correct custom would seem to be to eat the matza at the end of the day, i.e., on the night following the fourteenth of Iyar, as that is the time when they would eat the paschal offering in the Temple.

In some hasidic circles, it is customary for the Rebbe to hold a special meal, including words of Torah that focus on the nature of the day and its unique qualities. Some even conduct a kind of Seder on this night.

Further reading: For more on the Second Passover, see A Concise Guide to the Torah, p. 364; A Concise Guide to the Sages, p. 182; A Concise Guide to Mahshava, p. 314.

Further reading: For more on the Zohar, see A Concise Guide to Mahshava, p. 328. For more about Rabbi Akiva, his life and death, see A Concise Guide to the Sages, pp. 335, 364.