March Madness is about to begin.

The brackets for the 2019 NCAA Men's Basketball Tournament will be revealed Sunday starting at 6:00 p.m. EDT. 

Here are five things to know about Selection Sunday and March Madness.

Why do they call it March Madness? 

The year the tournament began in 1939, an Illinois high school official named Henry V. Porter referred to it as March Madness, according to the NCAA. However, it didn't become mainstream for another 43 years. Broadcaster Brent Musburger used it while covering the 1982 tournament and it stuck.

How many teams are selected for the NCAA tournament?

There will be 68 teams -- a significant increase from the eight teams that made up the first tournament in 1939.

Thirty-two teams get in automatically by winning their conference tournaments, no matter what their regular season record is. Yes, even the 8-22 Cal Golden Bears could have found their way in the mix if they had won the Pac-12 Tournament. (They didn't).

The other 36 spots are at-large bids that are selected by a committee weighing things like strength of schedule, road wins, etc. So, even though top-ranked Gonzaga lost in its conference tournament, the Bulldogs are still going to get into the NCAA Tournament.

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Eight teams that will be named Sunday will have to play in one of the "First Four" games on Tuesday and Wednesday of the opening week just to make it into the more traditional field of 64.

The final 64 are placed in four regions of 16 teams each, more commonly known as the "bracket." The regions are separated geographically. The lowest seeds in each region are pitted against the highest seeds (No. 16 vs. No. 1; No. 15 vs. No. 2; and so on).

A school in the 64-team field must win its first four games to reach the Final Four and all six to win the championship.

Who has been there the most?

The Kentucky Wildcats have been invited to the most NCAA tournaments with 58. However, they officially have 57 appearances. A recruiting scandal forced Kentucky to vacate its 1988 tournament appearance.

Forty-four teams have never made an appearance in March Madness, according to the NCAA. But two of those schools, North Alabama and California Baptist, have a pretty good excuse because they just transitioned from Division II to Division I play this season. However, the NCAA says they won't be eligible for the tournament until the 2021-2022 seasons. 

The team with the longest run of consecutive tournament appearances is the Kansas Jayhawks. They've been there every year since 1990 -- a streak of 29 years and counting.

UCLA has the most NCAA Tournament championships -- 11.

Will anyone fill out a perfect bracket?

When you hear the term "perfect bracket," it means correctly guessing the winner of 63 games before the tournament begins (people generally don't include the "First Four" games in their brackets).

The most commonly quoted odds of filling out a perfect bracket are one-in-9.2 quintillion (9.2 followed by 17 zeros). That's if you were to simply flip a coin for every game without putting any research into your decision.

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However, mathematicians have come up with formulas that show the chances are much better if the person filling out the bracket just does a little research. A Duke University math professor calculated it at 1-in-2.4 trillion. A DePaul University mathematician has it at 1-in-128 billion.

You have better odds at winning Mega Millions (1 in 302 million) than pulling off a perfect March Madness bracket.

It's only happened once

If you want to be the one person who picks a No. 16 seed to win a first-round game, more power to you. You should know the overall record for a 16-seed is 1-135. That one win came last year when Maryland-Baltimore County defeated Virginia 74-54. The next barrier to break? A No. 16 winning two games and getting to the Sweet 16.

This is what is known as a "bracket buster" because it's unlikely that someone filling out their bracket picked a No. 16 to beat a No. 1.