Amazon Prime Day doesn't exactly qualify as a national holiday, but it does come every year. And it's widely celebrated. And there are presents, kind of. Hmmm.

In case you've been living off-planet for the last three years, let's take a look at Amazon's "holiday of savings" and what you can expect this time around.

What is Prime Day?

Back in 2015, Amazon celebrated its 20th anniversary with a full day of discounts -- not just on Amazon-branded products, but on tens of thousands of other items as well. It was moderately successful -- okay, it was wildly popular -- despite some hiccups. 

In the years since, Amazon has worked to make more products and more inventory available (so items wouldn't sell out in minutes) and simplify the means of finding sale items.

Who can shop on Prime Day?

True to its name, Prime Day is for Amazon Prime subscribers only. If you're not a paid member, you can't take advantage of the deals.

As you may have heard, the company recently raised its annual Prime rate to $119. That's now the price for newcomers; existing customers will start paying the higher price as of June 16. Ah, but will Prime Day bring a Prime subscription deal? Read on.

When is Prime Day?

In years past, Prime Day has fallen sometime in mid-July. Last year, for example, it was July 11 -- though in 2017 it actually started the day before and lasted a total of 30 hours. (It's kind of like the way Black Friday now starts on Thursday.) "Prime Day Plus," anyone?

Although Amazon has yet to announce this year's date, the second Tuesday of the month is July 10, which is where I'm placing my bets. Of course, if the "extended plan" returns, that means it would actually start on Monday, July 9.

What kinds of deals can I expect?

There's little question that Prime Day will bring deals on many, if not most, of Amazon's branded products: Fire TV ($69.99 at Amazon.com) devices, Fire tablets, Kindle e-readers and of course every Echo.

Beyond that, look for a Black Friday-style assortment of deals in pretty much every category. There will undoubtedly be a few standouts -- in 2017, Amazon offered sweet deals on a Motorola Moto G5 Plus ($229.99 at Walmart) phone and a 55-inch 4K TV with built-in Fire TV, for example -- but don't get too carried away: Many of the discounts are no better than what you'll find in the average Amazon Gold Box daily deals.

Speaking of which...

How do I know if a deal is really a deal?

On the internet, every day is Black Friday -- and Cyber Monday, and Prime Day. That means you should approach every deal with a little bit of skepticism -- or at least a little bit of research.

One great place to start: CamelCamelCamel, the site that tracks Amazon price histories. (It can also notify you when Amazon products go on sale; here's how to use it to track Amazon Echo deals.)

Before you pull the trigger on any Prime Day deal, copy the URL, paste it into CamelCamelCamel's search field and check the results. You may discover that the product has indeed been priced lower in the past, and therefore may be again.

At the same time, consider using a browser plug-in such as Honey, which can instantly inform you if any third-party sellers have the same product for a lower price (which doesn't happen often, but it's worth checking).

Finally, be sure to check other sites. Best Buy, Walmart and other major stores may well trot out their own answers to Prime Day, offering loss-leader pricing on popular items.

How can I shop on Prime Day if I'm not a Prime subscriber?

As noted, you can't -- but you might be able to game the system a little bit. For starters, if you've never subscribed before, you can get a free one-month Amazon Prime trial. Sign up sometime in early July and you'll be able to shop Prime Day during the trial period.

It's even better if you're a student: Amazon has partnered with Sprint to offer college students a free six-month trial.

Finally, be on the lookout for a Prime subscription deal in the week or two leading up to Prime Day. Although it's questionable whether Amazon would offer such a deal so soon after enacting a rate increase, Prime Day's very existence is to help attract new subscribers. Thus, something like an $89 rate for new subscribers wouldn't be unthinkable.