Image Type

PSD: is the Adobe photoshop's file format able to edit only on this program. In other words the native Photoshop file. 
GIF: Is a picture file, it allows you to move pictures around and graphics as well. 
JPG: its where the images are been saved and store. Basically is the file of the compressed photo.
PDF: stands for portable document format. This file basically makes the file able to see just on another computer that has the same exact program that is why it is called "portable".
BMP: is one of the most common ones even though it is just another image file format.
PNG: It stands for Portable Network Graphics Files it almost works the same way as JPG but png don't usually gets the image affected by the compressed quantity.