The hosts associated with a numeric internet address can be optionally shown in netactview. The host is related with the website the application is communicating with but not always identical. The host won't tell you the exact web address the application is connecting to (Ex: for http://www.weather.com/weather/today you will see only www.weather.com). By default only the remote host is shown. See the View menu in order to toggle them on or off.
Many websites use host names that relate in non obvious ways with the actual web addresses you are typing in a browser. To get around that you can use the whois service. Netactview does not currently have whois integrated. In order to use whois just copy the remote address from netactview and use options like: Network Tools from Ubuntu (System/Administration/Network Tools/Whois), whois [ip address] command or online whois web sites.
The host name information is loaded separately from the connection information as it can take a few seconds. If a connection has an empty host name it was not already got, if the hostname is . there is not a host name for that IP address, else the string you see is the address associated host name.
If you use small refresh intervals you may be able to see netactview host name retrieval connections. They will be udp '53 domain' connections to your DNS server like: 'udp 42803 CLOSED 22.214.171.124 53 domain ns1-cache.ipv4ilink.net 441 netactview'.