What is an ISO

Actually, .iso, as talked about here in this thread refers to the file system used on cdroms for pcs. ( ISO-9660 )
http://alumnus.caltech.edu/~pje/iso9660.html

After it became obvious that cdroms were here to stay, software was developed to utilize cdroms and eventually cdrw & cdr. Eventually, software was made that could make an exact copy of a cdrom data at the sector level and store it all in an image file format called .iso. Many programs can utilize .iso files, usually cd burner software, backup apps like norton ghost, cad software, etc. There also are standalone simple apps that can create .iso images out of data on a floppy or a hard drive. These iso files can also be made in compressed format so as to require less hard disk storage space. Often movies, large sound files, large programs and even operating systems are made into .iso format for faster downloading and server efficiency.

There's an app called isobuster that you could use to view the contents of your iso image.

As for the name "ISO ", it's derivation comes from:

Short for International Organization for Standardization. Note that ISO is not an acronym; instead, the name derives from the greek word iso, which means equal. Founded in 1946, ISO is an international organization composed of national standards bodies from over 75 countries. For example, ANSI (American National Standards Institute) is a member of ISO. ISO has defined a number of important computer standards, the most significant of which is perhaps OSI (Open Systems Interconnection), a standardized architecture for designing networks.