Mass marketing is creating a product which appeals to all types of consumer. Mass marketing often ends up with the brand name being used instead of the product name e.g. Hoover not vacuum cleaner. Companies make use of global mass markets which means selling the same product with similar marketing techniques all around the world.
Niche marketing is aiming a product at a specific type of consumer. A niche market is usually a smaller segment of a larger market. Companies using a niche market often get less sales than they would if they aimed at a mass market so they have to make up for this by charging a higher price (as the product is often more specific to consumer needs, the customer is normally willing to pay more). It is easier for smaller firms to operate niche markets as there is less competition from bigger companies.