Short answers, pulled from the story.
Karma is the Sanskrit word for action or doing, coming from the root kṛ, meaning to do, make, perform, or accomplish. In Buddhist teaching it refers specifically to action driven by intention, cetanā, rather than to physical movement alone.
Karmaphala is the fruit or result of karma, also called karmavipaka, the maturation of a karmic act. The idea is drawn from agriculture, comparing an action to a seed that ripens only after a hidden interval has passed.
Good moral, intentional actions lead to wholesome rebirths, while bad moral actions lead to unwholesome ones. Giving to the Buddhist monastic order, known as dāna, became an increasingly important source of positive karma.
No, karma in Buddhism is not the same as fate or predestination. Its results are not a judgment handed down by a god, and a person always retains the freedom not to commit further unjust acts.
Baizhang's Wild Fox is Zen Buddhism's best-known koan on karma, about a teacher condemned to five hundred lifetimes as a fox for wrongly claiming an enlightened person does not fall into cause and effect. The Zen teacher Baizhang later frees him by answering that such a person is simply not in the dark about cause and effect.
Many Buddhist modernists equate karma with social conditioning rather than rebirth across lifetimes, and the scholar Dale S. Wright has proposed separating it from supernatural elements. The scholar Loy criticizes karma's use to rationalize suffering such as that of Holocaust victims, while other scholars argue the teaching does not assign blame to victims.