Burst rate photography
Burst rate is the number of consecutive shots a camera can take in continuous shooting mode.
When using this mode, images are stored in a high-speed buffer memory before being transferred to the memory card.
Once the buffer is full, the camera will reduce the FPS to give it enough time to free space. Burst rate can be affected by image formats, as it depends on the file size, as well as by the speed of the memory card used.
In a Nikon z7, the average RAW image size is 60Mb. You can expect 8 or 9 frames per second until the buffer fills (20 ish shots) then 3 to 5.5. fps.