Vulkan, previously known as Next Generation OpenGL or just GLnext, is a low-level, cross-platform graphics API from the Khronos Group.
Vulkan, once known as Next Generation OpenGL or just GLnext, is designed to be a low-overhead API that facilitates multithreaded 3D development, enabling different CPU threads to simultaneously prepare batches of commands to send to the GPU. It gives developers greater control of generating commands, putting tasks such as memory and thread management in their hands rather than relying on video drivers to handle these responsibilities. In so doing, it greatly reduces the amount of work that the driver must perform, though it increases the work of the application.
Correct API usage verification is performed by an optional validation layer, simplifying the driver.
Vulkan use SPIR-V as its standard language for graphics and compute shaders. The Khronos reference GLSL compiler compiles a form of GLSL (which implements a special extension to support Vulkan features) into SPIR-V, but users can use whatever compilers they wish which have a SPIR-V backend.
Vulkan is derived from AMD's Mantle API and shares some similarities with it.