Z-Test (depth test / ZTest) is a technical term that is extremely important in game graphics rendering and optimization (technical art). When the GPU draws a pixel, it compares it with the distance information already written to the depth buffer, determines whether it is in front or in the back, and processes occluding objects.
Real-world analogy: Physical occlusion in movie theater seats where you can't see the screen due to the head of the person in front of you
Z-Test (depth test) is a rule for determining whether or not you can see the screen from your seat in a movie theater. When you are about to sit down (when drawing pixels), use a ruler to measure whether a ``tall person (wall object in front)'' is sitting in front of you (Z value comparison). If there is someone in front of me, I will give up drawing and leave (skip drawing) because I can't see the screen. If there is no one in front of you, you will be seated safely and drawn on the screen.
depth buffer.