MD5SUM is an optional procedure to verify your download.
Large downloads can fail to download correctly and become corrupt. Hence it is worthwhile to check for any problems. Unfortunately this process is rather manual.
You may have noticed files with a .MD5SUM suffix such as:
webc-2.29.en.iso.MD5SUM
This is a file containing a checksum. This is to verify the downloaded image file is not corrupt. For example:
monty:~/images% cat webc-2.29.mini.iso.MD5SUM
9f65b24422bb92224f7c54bf911dad59 /home/hendry/www/mini/webc-2.29.mini.iso
monty:~/images% md5sum webc-2.29.mini.iso
9f65b24422bb92224f7c54bf911dad59 webc-2.29.mini.iso
Above the MD5SUMs match, which means the original checksum is the same as my local checksum. The image is now verified.