Information is reliable if you can trust it to be correct.
Credibility and objectivity are important here. Ask yourself the following questions to assess whether information is reliable:
What is the source of the information? Is it a book, magazine, database, website? What can you say about the reliability of that source? For websites, also pay attention to the domain name and the extension (.com=commercial, .org=organisation, .edu=educational institution et cetera)
Who is/are the author(s)? Are they experts? Is there an editor? Does the author work for an organisation, company or institution?
What is the purpose of the publication (to inform, convince, entertain, promote, sell)? Is there a client or sponsor?
If in doubt, search the internet for information about the author, organisation or publisher.