What is a Pixel 

A pixel is a basic unit of programmable of colour on a computer display or in a computer image.and a pixel in a single point in a graphic image for example if you get a picture and if you width or zoom into a picture it would get more pixelated.

I made this example of a picture from breath of the wild and I zoom up and it shows the picture getting pixelated when if you keep zoom in. 

Raster images-it digital images that composed of tiny rectangular pixels in order to represent the full images. if zoom in the picture it would get more pixelated.

Bmp-A bmp also known as the bitmap is a raster graphics images used to store bitmap digital images. 

GIF-A GIF (graphics interchange format)is when a picture is a move and it lots over.

Tiff- A TIFF (tagged image file format) is a flexible format that saves eight or sixteen bits per colour red, green and blue for 24 to 48-bit.

Jpg-a Jpeg (Joint Photographic Experts Group) mainly use for a photograph in digital cameras. it uses this file extension to store pictures. Although when it comes to file compression it does reduce the file size a little but can reduce the detail and some can be lost.

Vector images- Are digital graphic images which can be zoomed in and create 2 or 3 dimensions images it uses to control points and nodes. 

Psd-photoshop extension file when it is a PSD format you can edit as much as you want once it is compressed it is more difficult to edit.

Wmf-created for windows it can use and save both vectors and bitmap outdated and not used as much now.
Fla-(flash)it creates short movies and animations it very useful on web browsers.

Ai-to makes the images bigger, for example, boss level collision with boss makes it bigger.

Here is a video explaining what is a pixel