Describes an attitude, posture, or measure taken to protect oneself or one's position, often in contrast to being proactive or offensive.
His attitude is always defensive.
We need to adopt a defensive strategy.
防御的 is a near-synonym also meaning 'defensive', but 防衛的 often implies a broader, more strategic or psychological defense, while 防御的 can be more physical or protective.
Compound of 防衛 (defense) + 的 (-like, -ive).