Refers to a very light skinned person or a white man. It is pronounced with a nasalized "i", spelled Oyinbo, in Yoruba where the word originates and oyibo in Igbo speaking areas, it is generally used to refer to a person of European descent or people perceived to not be culturally African.
Pijin Example

Oyibo dey form Naija.

English Translation
The white man is pretending to be Nigerian.