Subsistence farming is to cultivate land for the purpose of feeding themselves and their families. Small land owners in developing countries or underdeveloped countries do that.
They eat the produce and sell or exchange excess produce for currecy or other goods needed to live. These farmers do not do farming as a business.
It is done in India in orissa, andhra pradesh, tamilnadu, west bengal, maha rashtra, uttar pradesh, bihar, jharkhad, etc. In the world, in countries of African continent, South American continent, Philippines, Sri Lanka etc.