Clean energy is a broad, non-technical term used in legal practice to describe energy generated with low or zero greenhouse gas emissions, typically from renewable or other low‑carbon sources (for example, wind, solar, hydro, tidal, geothermal, nuclear and, in some contexts, carbon capture and storage–enabled generation). It is widely used in contracts, project finance, regulatory advice and M&A relating to energy and infrastructure.The expression “clean energy” itself is not a consistently defined legal term in UK or Irish legislation or case law. Statutes and regulations instead use more precise concepts such as “renewable energy”, “low-carbon electricity”, “zero-emission vehicle”, “energy efficiency” or “sustainable investment”. Accordingly, practitioners should rely on the specific statutory or contractual definitions rather than assuming that “clean energy” has a fixed legal meaning.Usage is broadly consistent across England and Wales, Scotland, Northern Ireland and Ireland, where the term is commonly associated with climate change targets, net zero strategies, support schemes (such as Contracts for Difference or renewable support auctions), planning and environmental permitting, grid connection, and green or sustainability-linked finance.