Rollback. Doorbuster. Blowout prices. Do those words mean anything anymore?

Even Black Friday is fast getting lost in the blur of perpetual discounts as some of the nation’s biggest retailers go head-to-head Wednesday in a new midsummer event — yet another addition to an annual sales calendar packed with sales, sales and more sales.

Amazon, the online juggernaut that has been upending brick-and-mortar retailing for years, set off the latest sales frenzy by announcing a sale for the site’s 20th anniversary on Wednesday. Its Amazon Prime Day, meant to attract more shoppers to its $99 free-shipping membership plan, promises “more deals than Black Friday.”

Not to be outdone, Walmart swiftly announced an event of its own the very same day, with “thousands of great deals” and free shipping on orders of $35 or more on Walmart.com — and, in a jab at Amazon, no membership required.

“We’ve heard some retailers are charging $100 to get access to a sale,” Fernando Madeira, chief executive of Walmart.com, said on a company blog. “But the idea of asking customers to pay extra in order to save money just doesn’t add up for us.”