WARC files are raw recordings of crawler runs, including HTTP headers and other metadata. The raw, archival result of the downloads, that you can extract the files downloaded from.
During my time at the Internet Archive when we were working the wayback machine and related stuff, we wrote an arc/warc python library to parse and unpack these files. The library is over here https://github.com/internetarchive/warc. Just in case anyone is interested.
