士气也称为团队精神，是指一个团队的工作气势和氛围，它用来描述个体或群体在维护共同信仰和目标时，表现出来的努力、斗志和效率。团队精神一词适用于军队或团队运动的成员，也适用于商业或任何其他组织方面，特别是在压力和争议下所展现出来的气势。我们可以通过个人在履行义务时，所表现的意志、服从和自律等价值观来判断士气，更准确的话，则是个人在集体利益下所展示的信念、心态和动机。

在军事学中，士气有双重意义，其一是军士的作战士气，其二是部队的整体团结和凝聚力。一支部队如果拥有良好的设备、健全的补给线、空中掩护和明确目标，同时指挥官以身作则的话，整体而言，就会凝聚良好或高昂的士气。从历史上来看，精英军事单位如特种部队之所以士气高昂的原因，是因为他们的军纪严明，对所在部队的设施和培训感到自豪。当一支部队的军容散漫，士气相对低迷的时候，意味着它已经接近分裂和阵败的地步，晚清海军在「甲午战争」的作战即是例子。值得注意的是，通常指挥官并不注重军士的个人意志，而是部队的整体作战精神。

Morale (also known as esprit de corps (French pronunciation: ​[ɛspʀi də kɔʀ])) is the capacity of a group's members to maintain belief in an institution or goal, particularly in the face of opposition or hardship. Morale is often referenced by authority figures as a generic value judgment of the willpower, obedience, and self-discipline of a group tasked with performing duties assigned by a superior. According to Alexander H. Leighton, "morale is the capacity of a group of people to pull together persistently and consistently in pursuit of a common purpose". Morale is important in the military, because it improves unit cohesion. Without good morale, a force will be more likely to give up or surrender. Morale is usually assessed at a collective, rather than an individual level. In wartime, civilian morale is also important. Esprit de corps is considered to be an important part of a fighting unit.