To override a base view file in Magento 2, create a file with the following name:  app/design/frontend/[VendorName]/[theme]/Magento_Tax/templates/pricing/adjustment.phtml.

base folder is a default fallback for all arias used to share resources across areas.

More tips from Magento 2 Developer’s Cookbook

Source (Magento Stackexchange Question)(KAndy)