The original version of Barbara Winter’s book, Making a Living Without a Job, came out in 1993, and in it, she recommended creating multiple "profit centers," as opposed to building a single income stream. Over ten years later,  Robert Allen, the real estate entrepreneur, also wrote a couple books promoting the idea of multiple streams of income. Back then, building more than one source of income was difficult, time-consuming, and expensive. Fortunately, things have changed today. The Internet has made it easier, faster, and more affordable to generate multiple income streams.
The gems and jewellery industry has been economically active in India for several thousand years.[187] Until the 18th century, India was the only major reliable source of diamonds.[183] Now, South Africa and Australia are the major sources of diamonds and precious metals, but along with Antwerp, New York, and Ramat Gan, Indian cities such as Surat and Mumbai are the hubs of world's jewellery polishing, cutting, precision finishing, supply and trade. Unlike other centres, the gems and jewellery industry in India is primarily artisan-driven; the sector is manual, highly fragmented, and almost entirely served by family-owned operations.
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.