The nrf52810_pca10040 board is a modified version of the nRF52-PCA10040 that enforces the limitations imposed by the nRF52810 IC, which is a cost-reduced variant of the original nRF52832. Since Nordic does not offer a development kit for the nRF52810 you can use this board to develop for this IC while using the nRF52 Development Kit (PCA10040).

See nRF52-PCA10040 for more information about the development board and nRF52810 website [1] for the official reference on the IC itself.