Estimated wins

Each giveaway you enter raises your Estimated wins by x amount depending on how many people enter a giveaway. Eg: If you're the only person who enters (by some crazy chance) it will raise by 1.0; if a few thousand enter, the amount it raises will be very very small. Basically the higher the number of entrants in a single giveaway the lower your chances of winning and the less it goes up. It's pretty much just a way to keep track of your luck. :)

Also, welcome to the site!

It's a statistic, a sum of all the percentual chances you had to win a game from all giveaways entered, shows you if you've been lucky or not.

You for example have been very lucky !

According to CG, "Estimated wins is the sum of all your entered giveaways using the following formula... SUM(1/MAX(1,(Gift.Entries/Gift.Copies)))", which is the most formal way to say the same thing kralizeh and Aly have already answered. =]