This refers to a digital camera. In the days of the film cameras nobody worried about this.
In digital imaging, a pixel (or picture element) is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles. Each pixel is a sample of an original image, where more samples typically provide more-accurate representations of the original. The intensity of each pixel is variable; in color systems, each pixel has typically three or four components such as red, green, and blue, or cyan, magenta, yellow, and black.
The word pixel is based on a contraction of pix (“pictures”) and el (for “element”).
When you take a picture the elements of light (Red,Green & Blue) are stored in a form of media. This media is normally an SD or other card. These are very small and can store quite a few pictures. The number of pictures that can be stored on the card depends on the storage size and the resolution (explained below) the camera is set on for that picture.
The number of resulting pixels in the image determines its “pixel count”. For example, a 640×480 image would have 307,200 pixels, or approximately 307 kilopixels; a 3872×2592 image would have 10,036,224 pixels, or approximately 10 megapixels. The higher the megapixals the sharper a printed picture will be. In earlier cameras that were only 2 Megapixal you could only print picture 5×7 if you wanted them to look sharp. In today’s cameras (10 or more Megapixels) you can easily print very large pictures. If you would have printed a large picture with the old cameras the picture would be “pixelated” and would be very blurry.
The pixel count alone is commonly presumed to indicate the resolution of a camera, but this is a misconception. There are several other factors that impact the resolution. Some of these factors include sensor size, lens quality, and the organization of the pixels (for example, a monochrome camera without a Bayer filter mosaic has a higher resolution than a typical color camera). Many digital compact cameras are criticized for having excessive pixels. Sensors can be so small that their ‘buckets’ can easily overfill; again, resolution of a sensor can become greater than the camera lens could possibly deliver.
It should be noted that the higher the resolution the more storage it will take up both on your storage media and on your computer. You should know what you plan to use the picture for. As an example: if you plan to use it for a web site you can take it at a very low resolution. If you plan to publish the picture in a magazine (or other printed media) you need to have it as high as possible. Keep in mind that if you have your camera set at a high resolution you will not be able to store as much on your media card.
Media ports are now available on many computers and printers. You don’t have to use the hardware that came with your printer in that case.
As you can see this can become very complex. You can easily go to a search engine to find out more information about this subject.