Compassion is a sense of shared suffering, most often combined with a desire to alleviate or reduce such suffering.
Compassionate acts are generally considered those which take into account the suffering of others and attempt to alleviate that suffering as if it were one's own. In this sense, the various forms of the Golden Rule are clearly based on the concept of compassion.
Compassion differs from other forms of helpful or humane behavior in that its focus is primarily on the alleviation of suffering. Acts of kindness which seek primarily to confer benefit rather than relieve existing suffering are better classified as acts of altruism, although, in this sense, compassion itself can be seen as a subset of altruism, it being defined as the type of behavior which seeks to benefit others by reducing their suffering.
The cultivation of compassion is considered a virtue in many philosophies and also in almost all major religions , perhaps most notably in Buddhism, which, being based on the idea that "unenlightened life is suffering" (the First Noble Truth), seems fundamentally based on the concept of compassion. The example of Christ has also inspired Christians throughout history to found hospitals and other such institutions. Compassion can also be kindness towards a stranger that is unexpected in most situations. It has a link to generosity.