The ICANN stipulates that valid contact information must be provided when a domain name is registered. Indeed, that information will be used to get into contact with the domain name, and if there is no response, the domain name may be cancelled. That information can be publicly consulted using WHOIS tools (whois.eus, for example). That is why the privacy of these data is a concern for some individuals who have a domain name.
If one wants to conceal the information used when registering, WHOIS privacy can be used. This service provides a means of masking the information used to register the domain name, and even though the true information is saved, when the consultation is run, the information that appears will be different (the most usual thing is for the registrar’s data to appear). If you want to keep your data private, get in touch with your registrar and they will give you further information.