A term that refers to the number of pixels on a display or in a camera sensor (specifically in a digital image). A higher resolution means more pixels and more pixels provide the ability to display more visual information (resulting in greater clarity and more detail).
Resolution does not refer to the physical size of the display, camera sensor or image. For example, two displays with the same resolution can have different physical dimensions. And since there will be more pixels per inch on the smaller one, the image provided by it should be clearer and more detailed (although graphics will be physically smaller).