what do the numbers for each variation in chess opening mean by?

I assume you mean ECO code? It is a way of organizing chess openings for storage purposes and organization

https://en.wikipedia.org/wiki/List_of_chess_openings 

I don't see "million+" but do you mean something like this? The large numbers near the move indicate how many games in the database reached this position (variation) and the percentages afterwards reveals how well each sides scores in practice. 

For example: in my screenshot, 1. e4 c5 has 603,239 games in the database. 37% of the time White won, 29% of the time it was a draw and 34% of the time Black won. 

To add on to what was already said, keep in mind that in the above example, White specifically WINS 37% of the time.  The Sicilian does not result in a 37% score for White.

Often times, you'll see books reference that say, Black scores 45% with a given opening.  That does not mean he wins 45% of the time.  Don't forget, a win is 1 point, a draw is half a point, so to determine what each side scores percentagewise, you have to take the win percentage and add HALF of the draw percentage.

So, in this specific database of over 603 thousand Sicilian games, White scores 51 1/2 percent (37 + 0.5*29) = 37 + 14.5 = 51.5%  Black, therefore, scores 48.5%, which you can check the math via 34 + 0.5*29 = 34 + 14.5 = 48.5%.

Now this is based on one database - you look at another database, and the score will shift.  For example, in most databases I've seen, the Sicilian tends to score 52% for White and 48% for Black.  Also, those percentages you see are rounded to the nearest whole number, so it is possible that it actually is 52% rather than 51.5% due to rounding error.

Best way to get the exact number is to find the number of games won by each side and drawn.  The exact percentage would be (for White):

(White Games Won + (0.5 * Games Drawn)) / 603239

Would the number next to the openings be just for the day or is it a different amount of time since these positions are reached much more than 600,000 times in the history of chess.com.

@7

603,239 is only for master games.
It is total games.

thank you so much!

In addition, this is based on what the chess.com database has captured. This does not have every game that the 2023 MegaBase has. NOWHERE NEAR!

And so the numbers can be slightly off. The fewer the games the higher the variance.

For example, the Dicilian here verses the Sicilian in Megabase may be off by half a percent from one another.

Bitd's Opening, with far fewer games, may vary by 2 or 3 percent between databases.

Also, do not get so hung up on database percentages. Many of these games were played hundreds (plural) of years ago. There might be a hand full of games with 1.e4 e6 prior to 1834. Nobody knew the theory at all then. The French team in 1834 against the British basically put the French on the map then. By 1850, the French has been played, but to say known theory in 1850 is anything like known theory in 2024 would be ridiculous. So a game played in 1879 with 1.e4 e6 should be taken with a grain of salt compared to 1.e4 e6 in say, 2022.

It is like politics. Polls, specifically. If you look at one database and the French scored 47.3% for Black and another database the French scored 46.9%, and if day, you filter only games played since 1980 and it scores 46.8%, it is all within the "Margin of Error".

I know

It means the positions have been reached 1million+ times and the percentages mean, from left to right, White's win rate, the draw rate, and Black's win rate.