Ask ten times “What is a well?” and you might get ten different answers. People think of a well in terms of their workflows and experience. A reservoir engineer, production accountant, landman, field operator, business executive, and data manager all have different perspectives. Semantics (the contextual meaning of a word) can cause miscommunication within and beyond an organization. To address this issue, a PPDM Association Work Group, sponsored by several operating companies and data vendors, created baseline definitions for important well components in 2014. These definitions have become the foundation to analyze the terminology used by regulatory agencies around the world. This booklet presents the baseline definitions for the Well Components across the Well life cycle. As changes to the industry have come about, this Evergreen Work Group is proposed to revisit the work done in the last iteration of What is A Well and update it as appropriate.