CRC-verified files are files that have been tested on file corruption. If you download a file, then you should always make a CRC check on it (provided that a CRC hash was shipped with the file), to prove that your file is a perfect match for the original file. If the CRC check of a file fails, the file may have been changed or your file has been corrupted by the transfer or was bad to begin with. (It happens more and more for groups to spread crc corrupt files.) As a result, the corrupt file (e.g. videos, zip etc) might not be able to open/play or be of any use at all. If you have a corrupt file, you should either redownload it completely or request a patch for it, via a tool such as Zidrav or QuickPar.