So, what is Niche Marketing? Lots of internet marketers are making money online, because they know their target market. They do surveys on certain markets before selling products and offering their services. It means, they target certain people who are most interested in that particular product or service and not to the world in general, that's niche marketing.

And according to wiki:
A niche market is the subset of the market on which a specific product is focusing; therefore the market niche defines the specific product features aimed at satisfying specific market needs, as well as the price range, production quality and the demographics that is intended to impact.
Most big businesses use niche marketing. For example, a company like Hewlett Packard that makes computers and computer accessories might advertise all-in-one copy/printer/scanners to the home computer user while at the same time advertising single function machines to large businesses.

One of the things that make niche marketing so attractive to sellers is that their advertising budgets go further. It costs less to advertise to a specialized market than it does to advertise to a broader market.

Niche marketing must be designed to meet the unique needs of the targeted audience. Niche marketers must tailor their product to meet those unique needs. If, for example, you have designed a product to make landscape gardening easy enough for the untrained professional to do it, those who want to make their garden beautiful but didn't have a budget to hire a professional gardener will be most interested in your product.

For example, you'd discovered a certain ways on how to earn money online, then you can write an e-book explaining on how you do it and how to start and succeed an online business, which is a big hit for beginners.

Niche marketing is a very effective and cost efficient way to advertise and sell specific products or services to a specific audience, and hopefully, buyers of that product or service. People who are looking for that information are your niche market, and those who had already earned passive income online and not interested on what you're selling are not your target.