Compassion is a sense of shared suffering, most often combined with a desire to alleviate or reduce such suffering. Its cultivation is considered a virtue in almost all major religions and also in many philosophies, perhaps most notably in Buddhism, which, being based on the idea that "life is suffering" (the First Noble Truth), seems to be fundamentally based on the concept of compassion. 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 in 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.