Optical image stabilization uses gyroscopic sensors to detect the vibrations of the camera. The lens adjusts the optical path accordingly, ensuring that any type of motion blur is corrected before the sensor captures the image.
The number of megapixels determines the resolution of the images captured with the main camera. A higher megapixel count means that the camera is capable of capturing more details. However, the megapixel count is not the only important element determining the quality of an image.
A bigger variety of brand lenses means that you have more options and can find one that suits your needs.
With a higher light sensitivity (ISO level), the sensor absorbs more light. This can be used to capture moving objects using a fast shutter speed, or to take images in low light without using a flash.
A BSI (backside illuminated) sensor is a camera image sensor which captures better quality images in poor lighting conditions, and offers better overall sharpness and image quality.
CMOS image sensors are slowly replacing CCD sensors, due to reduced power consumption and better image quality. They can be very compact and cost relatively little to produce.