Historically, India has classified and tracked its economy and GDP in three sectors: agriculture, industry and services. Agriculture includes crops, horticulture, milk and animal husbandry, aquaculture, fishing, sericulture, aviculture, forestry and related activities. Industry includes various manufacturing sub-sectors. India's definition of services sector includes its construction, retail, software, IT, communications, hospitality, infrastructure operations, education, healthcare, banking and insurance, and many other economic activities.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.