The word "sushi" is often ambiguous for non-native Japanese. We think of it as being interchangeable with raw fish. Sushi is vinegared rice topped with other ingredients. Sashimi, which is slices of raw fish alone, is not sushi because it isn't accompanied with rice. Originally, sushi was fermented fish with rice preserved in salt, and this was a staple dish in Japan for a thousand years until the Edo Period (1603 to 1868) when contemporary sushi was developed. The word "sushi" means "it's sour," which reflects back to sushi's origins of being preserved in salt.