Northbound and southbound interfaces relate to computer servers.
A southbound interface decomposes concepts in the technical details, mostly specific to a single component of the architecture. Southbound interfaces are drawn at the bottom of an architectural overview.
Northbound interfaces normally talk to southbound interfaces of higher level components and vice versa.
These terms are generic in the sense that they are uniformly used over all layers of a computer application, i.e. independent of the fact that the computer system is about hardware, GUI, middleware etc.
A northbound interface is typically an output-only interface (as opposed to one that accepts user input) found in carrier-grade network and telecommunications network elements. The languages or protocols commonly used include SNMP and TL1. For example, a device that is capable of sending out syslog messages but is not configurable by the user is said to implement a northbound interface.