Pity is an emotion, usually resulting from an encounter with an unfortunate, injured, or pathetic person or creature. A person experiencing pity will often take mercy on the person/creature, giving them aid or money. Many people pity the homeless, orphans, the terminally ill, and victims of rape and torture.
Because pity will result in people aiding the pitiful, most people consider it a positive thing. Philosopher Friedrich Nietzsche, however, believed that pity causes an otherwise normal person to feel the suffering of others; "Pity makes suffering contagious," he says in The Antichrist. He felt that it is important not to make oneself feel superior to the person you are taking pity on. This imbalance could result in retailation against the help. People value their sense of pride, and pity can negatively affect the situation.
Often, the word is used alone in speaking to refer to something unfortunate. The full sentence is "It's a pity," but saying the word alone (as in "Pity.") conveys the same idea as the sentence.