Understanding DSLR/Mirrorless Camera Resolution
The following information applies mainly to traditional DSLRs (digital single lens reflex cameras) or newer mirrorless interchangeable camera systems.
IMAGE RESOLUTION
Image resolution is the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail. More image details means a clearer, sharper image overall.
PIXEL RESOLUTION
Resolution is the capability of the sensor to observe or measure the smallest object clearly with distinct boundaries. There is a difference between the resolution and a pixel. A pixel is actually a unit of the digital image. Resolution depends upon the size of the pixel. With a given lens setting the smaller the size of the pixel, the higher the resolution will be and the clearer the object in the image will be. Images having smaller pixel sizes occupy more space on the disk.
Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).
source: Wikipedia
MEGAPIXELS IN A NUTSHELL:
Digital cameras capture images as picture elements, known as pixels. Simply put, a megapixel is equal to one million pixels.
Digital images are made up of thousands of these tiny, tile-like picture elements. The more pixels, the higher the image resolution.
Minimum megapixels for quality prints at 300 dpi are as follows:
source: DigicamHelp