Resolution

Sensor Resolution

   The number of effective non-interpolated pixels on a sensor is discussed in the topic about pixels. 
 
Image Resolution

   The resolution of a digital image is defined as the number of pixels it contains. A 5 megapixel image is typically 2,560 pixels wide and 1,920 pixels high and has a resolution of 4,915,200 pixels, rounded off to 5 million pixels. It is recommended to shoot at a resolution which corresponds with the camera's effective pixel count. As explained in the pixels topic, shooting at higher (interpolated) resolutions (if available as an option) creates only marginal benefits but takes up more card space. Shooting at lower resolutions only makes sense if you are running out of card space and/or image quality is not important.