What is an image file?

[damkend]

In Ez-Mode Picker (see screenshot attached) there are 6 options and 3 of them mention the term "image file".

 

My questions:

1.  What is an image file?

2.  What is the purpose of creating an image file? 

3.  How is an image file different from a regular file/folder? (i.e. write image file to disk vs write files/folders for disk)

 

Additional question:

1.  I burned a movie file to DVD+RDL using Windows DVD Maker and when the encoding process was complete the source file was gone, how come?

 

 

[LIGHTNING UK!]

http://en.wikipedia.org/wiki/ISO_image