The word "mahatma" is a title of extremely high respect amongst Hindus. Sanskrit for "Great Soul," this honorific title was given to Gandhi in 1914.
This word is generally used to show respect for a person who has proven themselves to be of immense wisdom and greatness, and is granted only to the most respected Hindus, similar to the process of sainthood and canonization in the Christian tradition. Other translations indicate that this word means "venerable" or "high-souled." In other words, the mahatma is viewed as someone whose soul is pure. Hindus are deeply religious people and believe in the power of kindness and love. Thus, a mahatma would be heralded almost as a deity themselves.