Per NV official website : starting with NV GTX 600 series and later, every application and game runs at a guaranteed, minimum Base Clock speed. If there’s extra power available, a Boost Clock is enabled increasing clock speeds until the graphics card hits its predetermined Power Target. This dynamic clock speed adjustment is controlled by GPU Boost, which monitors a raft of data and makes real-time changes to speeds and voltages several times per second, maximizing performance in each and every application.​

https://www.nvidia.com/en-us/geforce/technologies/gpu-boost/technology/​

NVIDIA GPUs have various features that impact their base clock, including GPU Boost, which increases performance by utilizing power headroom to boost core and memory clock rates when sufficient power and thermal headroom are available. ​

https://developer.nvidia.com/search?q=GPU+BASE+CLOCK&page=1&filters=techblogs​