Whois is a protocol that is access to registering information. You can reach when the website was registered, when it will be expire, what is contact details of the site with the following informations.
In a nutshell, it includes these informations;
# Hello 2600:3c03::f03c:91ff:fe70:15f. Your session has been logged.
# Copyright (c) 2002 - 2019 by DK Hostmaster A/S
# The data in the DK Whois database is provided by DK Hostmaster A/S
# for information purposes only, and to assist persons in obtaining
# information about or related to a domain name registration record.
# We do not guarantee its accuracy. We will reserve the right to remove
# access for entities abusing the data, without notice.
# Any use of this material to target advertising or similar activities
# are explicitly forbidden and will be prosecuted. DK Hostmaster A/S
# requests to be notified of any such activities or suspicions thereof.
Registration period: 1 year
Dnssec: Unsigned delegation
# Use option --show-handles to get handle information.
# whois -h whois.dk-hostmaster.dk HELP for more help.