Today is Pesach Sheni. Pesach Sheni occurs every year exactly one month after Pesach. The historical purpose of this day was for those who were unable to bring theKorban Pesach on the correct date—because they were then Tamei or too far from Yerushalayim—to have a second chance to do so.
These days, due to the destruction of the lack of the Bais Hamikdash, Yidden are unable to perform the Korban Pesach, either on Pesach or on Pesach Sheni.
Some have the Minhag to mark this day by eating Matzah, in memory of the Korban.