I am rendering images for a product, but the guidelines are not very clear to me. The info says:

** "Main Image – min 1200 wide x 800 or up to 1600 high Thumbnail Image – 300 x 350 and limit of 50 kb weight/size. Thumbnail image should be a complete and accurate representation of the product. Promotional Image – 1200 wide x 325 high Additional/Lightbox Images - products must include at least 3 lightbox images when necessary - exceptions would be something like software – max 1000 wide x 1600 high"**

What is the difference between a "Main Image", a "Promotional Image" and "Additional/Lightbox Images"? Thanks in advance for your time!