安康 is a formal, somewhat literary expression meaning 'safe and healthy' or 'in good health'. You'll most often encounter it in written blessings and formal greetings — especially around holidays like 春节 (Spring Festival) or 中秋 (Mid-Autumn Festival). It's more elevated than everyday 健康 and carries a wish for both bodily health and overall well-being. Common collocations: 身体安康, 安康幸福, 祝您安康.