wikipedia.org/wiki/Vulkan_(API)
Probably oversimplified, Vulkan is the new OpenGL, which also provides low level access to hardware. No real use for Vulkan today, other than demos, but some folks running AMD graphics are reporting better performance in some games with the Vulkan driver installed on top of the latest hotfix driver [16.1.1]. Some are also reporting long-term problems in some games appear fixed after adding the AMD Vulkan drivers. This **might** be due to reported better support for OpenGL versions earlier than Vulkan. I don't know if gamers using Nvidia hardware are seeing similar results, but it may be worth a look, whether you're running AMD or Nvidia, to find out if Vulkan drivers are doing anything for the games you play.
OpenGL is similar to Direct X, allowing software to access hardware with Windows sort of stepping out of the way for increased performance, & it is used by some games. When I talk about Vulkan providing lower level access, that won't likely do anything for you directly, but is advertised as meaning more games in the future, e.g. it could be easier to port console games over to Windows.