Amazon Prime Day, the made-up holiday that rivals Black Friday, is coming soon. Here's why it's such a big deal.

Ted S. Warren/AP

Amazon Prime is increasingly important to the company.

• Amazon Prime Day is the company's middle-of-July sales bonanza.
• It offers steep discounts on a variety of products, similar to a Black Friday or Cyber Monday sale.
• In 2018, Prime Day became the largest sales event in Amazon's history, but it was leapfrogged by Cyber Monday later in the year.
• We still don't know when Prime Day 2019 will be, but we have a guess.
• Visit Business Insider's homepage for more stories.

Amazon Prime Day is coming.

The made-up holiday, when the retailer boasts Black Friday-like discounts exclusively for Prime members, is almost always held in the middle of July.

Last year, Prime Day was Monday, July 16. This year's date is still unannounced, but it could begin on July 15 if Amazon keeps to last year's schedule. Amazon's website for Prime Day says only that it is coming soon. An Amazon spokesperson did not immediately return Business Insider's request for further detail.

Prime Day is now in its fifth year - it started in 2015 - but it has grown quickly. It's now one of the biggest sales days on Amazon's calendar, rivaling Black Friday and Cyber Monday in importance.

Last year, Amazon kicked off the 36-hour Prime Day event with a bang, with its site nearly immediately crashing. It remained down for nearly an hour.

Read more: Amazon crashed for over an hour on its biggest shopping day of the year, likely losing millions in sales

At the time, Prime Day was the biggest shopping event in Amazon's history, with shoppers in the US gobbling up Amazon's own devices, like the Fire TV Stick, the Instant Pot, the 23andMe DNA test, and the LifeStraw.

It was handily beat as a single sales day by Amazon's 2018 Cyber Monday sale, according to the company.

As Prime Day grows larger, its importance grows as well. Prime is increasingly important to Amazon, as members tend to purchase more items and more frequently.

Amazon also keeps adding new services and perks, like Prime Day, to keep members happy in the ecosystem.

"Prime delivers such massive scale and features that we believe it would be very difficult for any company to replicate and compete against, and Amazon continues to expand and add more value to Prime by adding new benefits and growing existing offerings," JP Morgan analysts wrote in 2018, arguing that Prime is actually worth $785 a year.