The difference between policies, guidelines, and essays on Wikipedia is obscure. There is no bright line between what the community chooses to call a "policy" or a "guideline" or an "essay" or an "information page".
This explanatory essay itself is a supplemental page, which is an even more ambiguous group. Essays, supplemental, help (how-to), information and template documentation pages generally have a limited status during deliberations as they have not been thoroughly vetted by the community through the policy and guideline proposal process. However, some essays and supplemental pages are widely accepted as part of the Wikipedia gestalt, and have a significant degree of influence during discussions.
How-to and information pages typically provide technical and factual information and are not often referenced during deliberations, but rather used for directing editors to pages about Wikipedia's processes and practices.