Cowardice, in general terms, is the perceived failure to demonstrate sufficient robustness in the face of a challenging situation. The term describes a personality trait which is viewed as a negative characteristic and has been frowned upon within most, if not all global cultures, while courage, typically viewed as its direct opposite, is generally rewarded and encouraged.
Cowards are usually seen to have avoided or refused to engage in a confrontation or struggle which has been deemed good or righteous by the wider culture in which they live. On a more mundane level, the label may be applied to those who are regarded as too frightened or overwhelmed to defend their rights or those of others from aggressors in their lives.

Military law

Acts of cowardice have long been punishable by military law, which defines a wide range of cowardly offenses including desertion in face of the enemy and surrendering to the enemy against orders. The punishment for such acts is typically severe, ranging from corporal punishment to the death sentence. Cowardly conduct is specifically mentioned within the United States Uniform Code of Military Justice.

Etymology

According to the Online Etymology Dictionary, the word coward came into English from the Old French word coart (modern French couard), a combination of the word for "tail" (Modern French queue, Latin cauda) and an agent noun suffix. It would therefore have meant "one with a tail" — perhaps from the habit of animals displaying their tails in flight ("turning tail"), or from a dog's habit of putting its tail between its legs when it is afraid. Like many other English words of French origin, this word was introduced in the English language by the French-speaking Normans, after the Norman conquest of England in 1066.
The English surname Coward (as in Noel Coward), however, has the same origin and meaning as the word "cowherd".