It's been speculated for some time that the company would change the name of its desktop operating system from OS X to MacOS. The new name would match the operating system names for its other devices including iOS, tvOS, and watchOS.
The reference was spotted in the answer to "How does Apple conduct its Product Greenhouse Gas Life Cycle Assessment?"
Here it is:
To model customer use, we measure the power consumed by a product while it is running in a simulated scenario. Daily usage patterns are specific to each product and are a mixture of actual and modeled customer use data. Years of use, which are based on first owners, are assumed to be four years for MacOS and tvOS devices and three years for iOS and watchOS devices. More information on our product energy use is provided in our Product Environmental Reports.
It's likely that Apple would announce a name change at the company's Worldwide Developer Conference (WWDC) in June.