Clarification: Optical IS (image stabilization) refers to a technology used in a digital model for the purpose of reducing the blurriness when you snap a photo. Optical image stabilization is the most accurate one among three IS types, because camera shake is measured by a gyro-sensor. Based on this measurement, the sensor will be adjusted for compensating for the camera shake.
Optical image stabilization is different from digital image stabilization, which compensates for camera shake by using software corrections inside the camera. The optical IS is better than digital IS in terms of producing images of high quality.