Introduction:
The term Adivasi refers to the indigenous or tribal people of India. The word Adivasi was coined to refer to these people who were often marginalized and exploited by the mainstream society. In this question, we are asked who first used the term Adivasi to refer to these people.

Thakkar Bappa and the origin of the term Adivasi:
Thakkar Bappa, also known as Bhau Lokhande, is credited with coining the term Adivasi in the early 20th century. Thakkar Bappa was a social reformer who worked for the upliftment of the tribal people in India. He believed that these people were the original inhabitants of India and deserved to be treated with respect and dignity. Thakkar Bappa used the term Adivasi to refer to these people in his writings and speeches.

Usage of the term Adivasi:
The term Adivasi gained popularity in the 1930s and 1940s, especially among social reformers and activists who were working for the rights of the tribal people. Mahatma Gandhi, who was a strong advocate of the rights of the Adivasis, also used the term in his speeches and writings. However, it was Thakkar Bappa who first used the term to refer to these people.

Conclusion:
In conclusion, Thakkar Bappa is credited with coining the term Adivasi to refer to the tribal people of India. Although the term gained popularity in the 1930s and 1940s, it was Thakkar Bappa who first used it in his writings and speeches. The term Adivasi is now widely used to refer to the indigenous people of India and has become an important part of the discourse around their rights and welfare.