How does Buddhism define abortion? Abortion is a much-debated topic, and religion frequently plays a role in any such discussion.

How does abortion fit into Buddhist faith?  

Is it considered negative karma by definition, or perhaps negative karma, depending upon the situation (e.g. in a family that cannot afford to properly support and raise a new child, or in the case of an abortion to save the life of the mother)?

Are there definitions of when human life begins tied with Buddhism?
In Buddhism, life starts at the moment of conception. So abortion breaks the 1st precept and causes bad Karma no matter how you try to justify it. Even if the husband's intention is to save the wife(mother), it still causes bad Karma. To give you an analogy, let's say a bear captured your wife and is about to kill her. Say you have a gun with you. You can shoot the bear and save your wife, but it still breaks the 1st precept and causes bad Karma.