Acidic effluent or run-off; specifically (also more fully "acid mine drainage") the outflow of acid water from an area of oxidizable rock exposed to the air as a consequence of mining.
Origin
Late 19th century.
Definition of acid drainage in US English:
acid drainage
noun
Acidic effluent or run-off; specifically (also more fully "acid mine drainage") the outflow of acid water from an area of oxidizable rock exposed to the air as a consequence of mining.