Multi-tenancy
Imagine that you are building an invoicing application and you intend to adopt the Software as a Service (SaaS) model. Your application will certainly have products and clients who will order those products. You'll have to keep a record of this. So all in all, in such a minimal application, you will store clients, products, and orders.
However, there's no point if there's only one business or establishment that can use your system. You can't hope to make any profits that way, and you'd want more and more businesses to sign up and pay for it. In that case, every business will have a different set of products and clients and the orders that they will get.
The typical way around that situation is to have another table or model in your system with a name, organization, company or business. Every product, customer, or order that you create will have a reference to their corresponding organization. When someone signs up, you create a company/organization record and a user for them...