The argument -p80 --script http-enum tells Nmap to initiate the script http-enum if a web server is found on port 80. The script http-enum was originally submitted by Ron Bowes and its main purpose was directory discovery, but the community has been adding new fingerprints to include other interesting files, such as version files, READMEs, and forgotten database backups. I've also added over 150 entries that identify vulnerable web applications from the last two years, and new entries are added constantly.