Yosemite is the name of Apple's eleventh version of OS X, released on October 16, 2014. It follows Mavericks (OS X 10.9) and is also called OS X 10.10.
While it is normal for each new version of OS X to include slight modifications to the user interface, Yosemite presented the most drastic change in several years. The interface includes many translucent elements, in which objects are semi-transparent. It includes a more "flat" design than earlier versions of OS X with new icons and window styles that do not have a glossy finish. While the design is not as flat is iOS 8, Yosemite's updated style makes OS X and iOS more similar in appearance.
Besides altering the OS X interface to be more like iOS, Apple designed Yosemite to be more integrated with iOS as well. For example, the updated AirDrop feature allows you to share files directly with nearby iOS devices. Handoff allows you to work on something on your Mac and then resume work on your iOS device, and vice versa. The improved Messages app allows you to send and receive both iMessages and SMS messages using your Mac instead of your smartphone. You can even send an receive calls with your Mac by relaying them through your iPhone.
Yosemite also includes significant updates to OS X's traditional bundled apps, such as Safari and Mail. For example, Safari includes a built-in Share menu for sharing links on social media and provides its own search suggestions when typing keywords in the address bar. Mail allows you to mark up attachments before sending them, and includes Mail Drop, a service that allows you to send attachments email attachments up to 5 GB in size. In Yosemite, iCloud Drive is built into the Finder, which allows you to manage your iCloud documents the same way as your local files.
Like Mavericks, OS X Yosemite is available as a free upgrade from the Mac App Store. It supports most Mac models released in mid-2007 or later.