Understanding files and filenames

What are the definition of file, filenames, and extension?

File is a collection of data and information.
Filename is the label of the file.
Extension is found in the end of the filename. example: .doc, . jpg, etc.

in my own words:
Why is it important to assign a filename to your files?
It is important because when you have a filename it is easier to identify your file. If you don't have a filename you have to look into the data in the file to know what the file is about