I have never seen such a line in an /etc/hosts file, particularly the ::1 section, which should really be an IP address (though maybe that's shorthand for an IPv6 address of all-zeroes except for the last chunk, which is a one, and means localhost)
In fact, the more I think about it, it looks like the IPv6 equivalent of:
..which is the loopback address of all machines; except, I don't know how/where the "127" went to..
Typically the hosts file contains IP-to-name mappings, and optionally, alias(es) to those names, such as:
184.108.40.206 sillysite.com silly
So, you see the IP address, followed by the domain name, followed by an optional alias (short name). The hosts file usually contains lines in this format. But with IPv6, items between colons, that are zeroes, can be omitted.
EDIT: I edited the post after pondering the IPv6-ness of the line. You may want to Google up something like "IPv6 hosts file" and see what turns up.