Super Tuesday is the election day early in a United States presidential primary season (February or March) when the greatest number of U.S. states hold primary elections and caucuses. More delegates to the presidential nominating conventions can be won on Super Tuesday than on any other day, amounting to approximately a third of all delegates. It is therefore a strong indicator of the likely eventual nominee.
The particular states holding primaries on Super Tuesday have varied from year to year because each state selects its election day separately.
Tuesday is the traditional day for elections in the United States. The phrase Super Tuesday has been used to refer to presidential primary elections since at least 1976. It is an unofficial term used by journalists and political pundits.
In 2020, Super Tuesday will occur on March 3. Fourteen state primaries and the American Samoa caucuses will take place, amounting to 1357 pledged delegates—33.8% of the nationwide total.
Background
United States politics are dominated by two major political parties, the Democratic Party and Republican Party, which choose their presidential candidates in nominating conventions attended by delegates from states. State law determines how each party’s delegates are chosen in each state by either a primary election or a caucus and on what date those contests are held. State governments or state party organizations choose the date they want for their states’ primary or caucus. With the broadened use of the modern presidential primary system (following the chaotic 1968 Democratic National Convention in Chicago), states have tried to increase their influence in the nomination process. One tactic has been to create geographic blocs to encourage candidates to spend time in a region.
One motivation for the creation of Super Tuesday has been criticism and reform proposals of the current primary system, many of which argue for creating a National Primary or a regional primary, such as the Rotating Regional Primary System adopted by the National Association of Secretaries of State in 1999, among other proposals.
Sources and further reading:
What is Super Tuesday and why is it important?
https://www.washingtonpost.com/politics/2020/02/19/what-is-super-tuesday/?arc404=true
Your State-By-State Guide To Super Tuesday
https://www.npr.org/2020/03/02/811028381/your-state-by-state-guide-to-super-tuesday
Super Tuesday Could Show Just How Blue Texas Is Turning
https://www.npr.org/2020/03/02/810401130/super-tuesday-could-show-just-how-blue-texas-is-turning