Short answers, pulled from the story.
Aliyah is a Hebrew word meaning "ascent" or "going up." It refers to Jewish immigration to the Land of Israel, a journey traditionally described as an ascent both geographically and spiritually. Jerusalem sits at approximately 750 meters above sea level, making the climb literal for many early immigrants.
The Law of Return, passed by the Israeli parliament in 1950, grants all diaspora Jews and their children and grandchildren the right to relocate to Israel and acquire citizenship based on their Jewish identity. It is the legal framework that supports and enables aliyah.
Since the Israeli Declaration of Independence in May 1948, more than 3 million Jews have made aliyah. In 1949 alone, 249,954 immigrants arrived, the largest single-year intake ever recorded. The total number of immigrants since 1882 recorded in historical data exceeds 3.8 million.
Aliyah Bet, also called Ha'apalah or secondary immigration, was clandestine Jewish immigration to Mandatory Palestine organized between 1933 and 1948 in defiance of British immigration quotas. It was organized by the Mossad Le'aliyah Bet and the Irgun, primarily by sea. During its 14 years of operation, roughly 110,000 Jews reached Palestine illegally.
Several airlifts and covert operations evacuated Jewish communities from Arab countries after 1948. Operation Magic Carpet, also known as Operation On Wings of Eagles, airlifted nearly the entire Jewish community of Yemen, about 49,000 people, between 1949 and 1950. Operation Ezra and Nehemiah brought approximately 120,000 Iraqi Jews to Israel. Egyptian Jews were smuggled out in Operation Goshen.
Yom HaAliyah, or Aliyah Day, is an Israeli national holiday that commemorates Jewish immigration to the Land of Israel. It began as a grassroots initiative in 2009 led by young immigrants in Tel Aviv. The Twentieth Knesset voted to codify it into law on the 21st of June 2016, placing it annually on the 10th of the Hebrew month of Nisan.