This refers to the color depth. It allows for over a billion colors, which reduces "banding" in dark scenes or gradients (like skies).
HEVC is "heavy" on the processor. If it lags, try enabling "Hardware Acceleration" in your player settings.
A modern, sleek player that handles HEVC files perfectly on macOS. 2. Understanding the Technical Tags
A compression standard that makes files much smaller than the older H.264 without losing quality.