a pictogram can be used to guide or instruct (eg a stop or no smoking sign). Icons are not so restrained in their design and do not need to conform to rules. Icons are seen in all areas of screen based technologies, they are on websites (eg shopping basket) and sofware (eg arrow cursor, waste bin etc...)

I would strongly recommend buying 'Pictograms, Icons and Signs' by Rayan Abdullah

http://www.amazon.com/Pictograms-Icons-Signs-Rayan-Abdullah/dp/0500286353

This has great definitions and all the information on pictograms and icons you could ever wish for.