Definition: Ahimsa

In Short: "Ahimsa or non-injury, of course, implies non-killing. But, non-injury is not merely non-killing. In its comprehensive meaning, Ahimsa or non-injury means entire abstinence from causing any pain or harm whatsoever to any living creature, either by thought, word, or deed. Non-injury requires a harmless mind, mouth, and hand." -Sri Swami Sivananda

At Length:

• Article from Yoga.com
• Of course, the Wiki