Final answer:
A buffer is a solution that resists changes in pH when acids or bases are added, essential for maintaining pH balance for chemical and biological processes.
Step-by-step explanation:
A buffer is a solution that includes a weak acid and its conjugate base or a weak base and its conjugate acid, which allows it to resist significant changes in pH when an acid or base is added. An example of a buffer is a mixture of acetic acid (CH3COOH) and sodium acetate (CH3COONa), which maintains its pH despite the addition of strong acids or bases. Buffers are essential for maintaining the pH balance needed for various chemical and biological processes.