When looking at the front side of a motherboard so that the I/O panel is at the left side of the motherboard, the north side will be the towards the top edge of the motherboard, south side will be towards the bottom edge, west towards the left and east towards the right: 

Historically, the northbridge was one of two main chips on the motherboard (northbridge and southbridge), and handled communication between the CPU, RAM and PCI(e) slots. 

Nowadays, this functionality is typically already integrated into the CPU, but the concept of “north”, “south”, “east” and “west” is still commonly used for orientation on a motherboard or CPUs installed on the motherboard.

Motherboards with a rotated layout

Some motherboards have the socket and RAM layout rotated by 90 degrees, but even in this case the north side will be at the top when the I/O connectors are towards the left.