Something is Gandhian if it's influenced by the philosophies and activism of Mahatma Gandhi, particularly his ideas about non-violent protest.
Mohandas Karamchand Gandhi, more popularly called Mahatma Gandhi, was an Indian nationalist who led protests against British rule during the early twentieth century. He is famous for achieving his political goals using non-violence and inspiring other activists to also use these Gandhian principals. Martin Luther King, Jr, for example, led the African-American Civil Rights movement using Gandhian ideals of protest without violence.