• 防止ぼうし — prevention
• 防犯ぼうはん — crime prevention
• 消防しょうぼう — firefighting
• 防衛ぼうえい — defense
• 予防よぼう — precaution

防 combines the radical 阝 (hill or mound) with the phonetic 方. Originally, it described an embankment or defense structure built along a river to prevent flooding. Today, it's widely used in contexts involving protection, safety, and prevention, from disasters to crime and disease.

このマスクは 風邪かぜを 防ふせぐために使つかいます。
This mask is used to prevent colds.

火事かじを 防ふせぐ設備せつびが 整ととのっています。
The building is equipped with fire prevention systems.

The primary reading is ボウ (bou), commonly used in compounds like 防止 and 防犯. The kun-yomi ふせぐ (fusegu) is used in more direct or literal expressions like “to prevent something from happening.”