Apple just renamed one of its oldest and most important products

Apple just changed the name of its original operating system for the first time since 1999 on Monday at its annual conference.

Say goodbye to OS X - and meet macOS, the new name for Apple's desktop operating system.

"I"m talking about the name OS X itself - it's been with us for over 15 years, and it's served us so well," Apple SVP Craig Federighi said. But times change, and now "the name of the world's most advanced desktop operating system is now MacOS."

macOS has been a key product for Apple since former CEO Steve Jobs returned to the company in 1997, bringing technology from NeXT. In 2001, the first desktop version based on NeXT was released under the name OS X - pronounced "oh ess ten."

Since then, Apple has released a new version of OS X every year, previously named after big cats, like leopards and cheetahs, and most recently named after scenic locations in California, like Yosemite.

This year's macOS is named "Sierra."

But Apple has released and developed several new platforms that have arguably surpassed macOS in importance, especially iOS, the software that makes iPhones run. On Monday, Apple announced the tenth version of iOS.

So to prevent confusion, Apple renamed its oldest operating system. The new name change also brings Apple's desktop brand in line with its other platforms.

The new name won't cause a big change to the way users use their Macs, but it may take a while for developers and users to get used to saying "OS X." But it's still the same stable operating system that Apple's been developing for the past 15 years.

The new MacOS will be a free update, and will become available this fall.