endo, exo, syn, anti

https://doi.org/10.1351/goldbook.E02094
Descriptors of the relative orientation of groups attached to non-bridgehead atoms in a bicyclo[x.y.z]alkane (xy > z > 0).
E02094-1.png
If the group is orientated towards the highest numbered bridge (z bridge, e.g. C-7 in example below) it is given the description exo; if it is orientated away from the highest numbered bridge it is given the description endo. If the group is attached to the highest numbered bridge and is orientated towards the lowest numbered bridge (x bridge, e.g. C-2 in example below) it is given the description syn; if the group is orientated away from the lowest numbered bridge it is given the description anti.
E02094-2.png
See also: syn, anti
Source:
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2207 (https://doi.org/10.1351/pac199668122193)