Gandhi is the best know historical practician. Ahimsa is a rule of conduct that bars the killing or injuring of living beings.
With the exception of the need for food, even insects and plants should be left unharmed. The principle can be extended to controlling your speech so as not to cause emotional harm. Injure none in thought, word, or deed.
Ahimsa takes strength of mind and character - it is an ideal that takes bravery, restraint and forgiveness.
The practice of Ahimsa leads to universal love, bliss and peace.