Pesach (Passover) falls on Nisan 14, the 14th day of the first Hebrew month. It is the foundational feast of the Hebrew calendar, commemorating God's deliverance of Israel from slavery in Egypt (Exodus 12). The Passover lamb's blood on the doorposts caused the angel of death to "pass over" Hebrew homes.
Christ Jesus IS the Passover Lamb. He was crucified on Passover, Nisan 14, CE 31 — a Hebrew Wednesday — fulfilling every type and shadow of the Levitical sacrificial system. His "Last Supper" was the Passover Seder meal, eaten after sundown on the beginning of Nisan 14.
See FAQ 03 — When Was Christ Jesus Crucified? and Easter, Passover & Pentecost Dates 2000–2050
The day following Passover (Nisan 15) is the first day of the seven-day Feast of Unleavened Bread — the first of God's three ordained Annual High Sabbaths (Pilgrimage Sabbaths).