A URL is a web address, the string of letters and/or numbers (usually starting with http or https) that lead you to a website. The letters after the final period refer to the website's Top-Level Domain (TLD) and is called a domain suffix (examples are .com or .org). These can tell you what the website is for, or who put it together, and help you decide if a website is reliable enough to use in your research.
What is it? One of the most common domain suffixes, .com signals a Commercial website. This is usually a website for a business or service, and its main objective is sales; many news websites are also .com sites. Domains ending with .net are less common, but similar.
Should I use it? Maybe. Many scholarly publishers have .com addresses! But most .com websites should be used with caution beyond basic information (contact info, mission/vision statements, etc.). Examine news websites very carefully for bias.
What is it? Websites ending in .org are Organization websites, usually for member organizations or nonprofits.
Should I use it? Analyze .org sites carefully. Many are biased toward a specific agenda they're pushing, and sometimes for-profit groups have a .org address. As with .com sites, basic contact information or mission/vision statements should be okay to use.
What is it? .edu signals a page from a College or University website.
Should I use it? Most .edu websites are considered reliable for research, but privately-owned pages from faculty or students might contain inaccurate information. Usually these websites have a ~ symbol somewhere in the web address.
What is it? Websites ending in .gov are pages from U.S. Federal, State, or Local Governments, including agencies; .mil websites contain information from the U.S. Military.
Should I use it? .gov and .mil websites are generally acceptable for academic research papers, but be sure to check what if any vetting process has been imposed on given reports.
What is it? Websites ending in other sorts of endings can be tricky. Ones ending with ".co" are frequently masquerading as a legitimate website that would end with a ".com" and should be treated with extreme caution! Sites ending with a country code (".us" for example) may be perfectly legitimate sites, or they may be fake sites as well. Be wary of spelling errors in URLs. It's common to see letters in a domain name replaced with numbers or similar-looking letter combinations: watch for the number 1 in place of the lowercase letter L and the lowercase letters "RN" in place of the letter "m."
Should I use it? If something looks sketchy, don't even click it. Definitely don't cite it.
You can make Google bring back results from specific domain suffixes by using the command site:.
After typing the word "site" followed by a colon (:), use the suffix with the period (for example, .edu).
EXAMPLE: PTSD site:.gov will return only those results about PTSD that are from .gov websites
You can also use the command to search Google for results from a specific website. In this case, the command would be site: followed by a full or partial web address.
EXAMPLE: PTSD site:www.ptsd.va.gov will return only those results about PTSD that are from the VA's PTSD website