Battery (All): Terminology: Corrosion
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
A destructive chemical reaction when metal is broken down in an aggressive chemical environment. Sulphuric acid, for example, is aggressive against iron. The iron breaks down and corrodes. The battery terminal is vulnerable to corrosion if it is not maintained correctly.