A geodetic datum is a coordinate system, and a set of reference points, used to locate places on the earth.
Basically, the Geo coordinate system is based on the assumption that the earth is a straight forward ellipsoid – but, just by walking around, you will notice that we have hills and valleys and that the surface is not that smooth. As Maths does not take into account that the surface is not flat, coordinates move around a little depending on where you are. For this and other concerns, people tried to discover the most proper datum system by referring different base points, shapes of the earth, encryption and etc.
The coordinate data in EPS database and API response are aligned with Google Maps coordinate system which bases on datum WGS-84.
It is necessary to make sure GPS devices/maps and coordinates data are using the same datum (eg. all GPS devices and maps are following GCJ-02 standard in mainland China by default). Using different datums will result in differences/shift in where the same set of coordinates is displayed on the maps.