The full forms for these categories in India are:

1. SC – Scheduled Castes – These are communities that have historically faced social and economic backwardness due to caste system. The Indian Constitution provides them with special quotas in education, government jobs, and other opportunities.
2. ST – Scheduled Tribes – These are indigenous communities who have traditionally lived in isolation. The Constitution provides them with similar benefits as Scheduled Castes.
3. OBC – Other Backward Classes – This is a broader category that includes communities facing social and educational backwardness, but not necessarily because of the caste system. They may be castes, communities, or ethnic groups.