What are volumes? (in reference to using winrar)

[whatevaz_cleva]

sometimes the people uploading the games screw up the volume names. one time i kept getting an error until i realised that there were 2 .r03 files. one was 345kb or some shit and the other was 14.9Mb. i changed the 345kb one to r04 and it worked. ##### the file sizes n stuff.