Maybe the real question you need answered is "What is an ISO image?"
An iso image (most basic desciption) is an image of a CD/DVD/Blu-Ray.
An ISO Loader would load this ISO image as if it were the original CD/DVD/Blu-Ray (and therefore the image would be playable like the original disk)
You know http://www.wikipedia.org is fantastic for descriptions of things, Google
is great for researching topics too and the PS3NEW search function is great if you want to find answers to PS3/PS2/PS1/PSP/Wii/DS/Xbox/Xbox360 etc etc questions.
You really should learn how to use the tools provided - it'll make your life a little easier, will open a wealth of knowledge to you and prevent backlash from annoyed regulars.