The Brahmo Samaj, also known as the Brahmoism, is a reform movement that originated in 19th century India. It was founded by Raja Ram Mohan Roy and Debendranath Tagore, with the aim of reforming Hinduism and promoting social and religious reforms in the Indian society.

The Brahmo Samaj was a response to the social and religious issues prevalent in India during that time, such as the caste system, superstitions, and rituals. The movement sought to establish a monotheistic form of Hinduism, based on the principles of reason, morality, and social reform.

The term 'Brahmo' is derived from the Sanskrit word 'Brahman', which refers to the ultimate reality or the divine force in Hinduism. The Brahmo Samaj believed in the existence of one supreme God, and rejected the polytheistic beliefs and practices of Hinduism. They also rejected the authority of the Vedas and other Hindu scriptures, and instead emphasized on the importance of individual conscience and reason.

The Brahmo Samaj emphasized on the moral and ethical teachings of Hinduism, rather than its ritualistic practices. They believed in the unity of all religions and promoted religious tolerance and harmony. The movement also advocated for the education of women and the abolition of the caste system, which was a major social issue in India at that time.

One of the key figures of the Brahmo Samaj was Raja Ram Mohan Roy, who is often referred to as the 'Father of Modern India'. He was a social reformer, a philosopher, and a scholar, who played a crucial role in the revival of Hinduism and the Indian society. He was a strong advocate of women's rights and worked towards abolishing the practice of Sati, which involved the immolation of widows on their husband's funeral pyre.

Debendranath Tagore, another prominent figure of the Brahmo Samaj, believed in the concept of 'Brahma Samaj', which refers to the universal brotherhood of all beings. He also established the 'Shantiniketan' school, which promoted a modern and holistic approach to education.

The Brahmo Samaj had a significant impact on Indian society, and its principles and teachings continue to influence various social and religious movements in India. The movement also paved the way for the emergence of other reformist movements, such as the Arya Samaj and the Ramakrishna Mission.

In conclusion, the Brahmo Samaj was a reform movement with monotheistic leanings, which aimed to reform Hinduism and promote social and religious reforms in 19th century India. It emphasized on the principles of reason, morality, and social reform, and played a crucial role in shaping the modern Indian society.