Rater than attempting to paraphrase or summarize it, I can refer you to the original. Turn to Exodus Chapter 12. Start at verse 1 and read for a while.
Passover is pesach, spelled פסח in both biblical and modern Hebrew.
Passover = Pesach (פסח)
In Hebrew it is: Chag Pesach sameach In English it is: Happy Passover
Passover is called "Pessa'h" in French. This is not a French word, but comes from Hebrew.
Passover always starts on the 15th of Nisan on the Hebrew calendar. It's the same date every year on the Hebrew calendar.
If you are asking what the Hebrew word for "Passover" is, it's pesakh (פסח). If you are asking for the meaning of the holiday, it is a celebration of freedom, commemorating the exodus from Egypt.
Passover always begins on the same date on the Hebrew calendar: the 14th of Nissan.
Passover is always celebrated at the same time on the Hebrew calendar, the 15th of Nisan. However, the Hebrew and Western calendars are not the same so Passover falls on different dates on the Western calendar.
Passover already is an English word. The Hebrew word is Pesach.
Pesach ba (פסח בא)
had gadya is not Hebrew. It is Aramaic for "one lamb" and is the name of a famous Passover song.
It symbolizes the beginning of The Passover.