Open web sources can be searched, typically using search engines such as Google, and are available on the internet without requiring authentication (such as user name & password, or a payment being made).
Because anyone can publish anything online, it is very important to take extra time evaluating these resources.
Research, technical, and statistical reports that are not formally published as books, journal articles, or in a formal manner by commercial publishers fall into the category of "grey literature." They are sometimes hard to find, but think-tanks, lobbying groups, government agencies and inter-governmental organizations often post this type of report on their websites.
It is important to be aware of any bias or point of view represented by the site. Following the funding sources can be helpful in determining this, particularly if the bias or point of view is not identified on the group's website.