Multi-Level-Marketing. Otherwise known as a pyramid scheme.

Strictly speaking, the two are different. A pyramid scheme doesn't involve the production or sale of actual goods or services, you're literally just rewarded for bringing other people in. An MLM will usually have a product that it sells in addition to rewarding recruitment. Theoretically, in an MLM, you can make money just by selling products.

MLMs are usually shady but are technically legal. Pyramid schemes are always illegal.

In other words, an MLM is adding toothpicks to a pyramid scheme to make it legal. The products are never worth the price and if you can make money by just selling them you don't need the MLM.