An EOC (Encyclopedia Of Chess)-file is a file that contains a great number of games that can be consulted by the user as well as by Rebel. If the consult window is activated you can read (at least at the start of a new game) some data (see section Consult window).
The EOC that is supplied to you on CD-ROM contains the data of Rebel's standard database of 300,000 games and are ordered in such a way that Rebel can quickly consult this data. Of course Rebel can do this even faster if the EOC is written on your harddisk. It takes some disk space though. If you want this you have to copy all files with EOC in it.