Today is Pesach Sheni, which occurs exactly one month after Pesach.
The historical purpose of this day was for those who were unable to bring the Korban Pesach on the correct date—because they were then Tamei or too far from Yerushalayim—to have a second chance to do so.
Some have the Minhag to mark this day by eating Matzah, in memory of the Korban Pesach.
It comes one month and one day after Pesach
Pesach Rishon is on the 15th of Nisan. Pesach sheninis on the 14th of Iyar .that’s less than a month