Poké refers to marinated raw fish salad and is pronounced POK-KAY not POK-KEE. Its origins are found in Hawaii where it's almost pervasive, found in local grocery stores to shacks on the beach. Poké itself means "to section, slice or cut" so don't get it confused with sashimi as it's often found in cubes versus slices.
Poké can have many different variations from the fish that is used to the garnishes its tossed in. In Hawaii, you can find 20 different types of pokés in the local market ranging from ahi tuna to tako (octopus) all tossed in ingredients such as soy, sesame, macadamia & seaweed. It's often served in plastic cups with a side of rice. Poké is often marinated hours before serving to allow the fish to seep in the flavors; this by no means devalues the quality of the fish, but rather allow you to get the full flavors and experience of traditional Hawaiian culinary style.