What is the relationship between securities companies and brokers?

Brokers and securities companies are the same in a broad sense and a little different in a narrow sense.

Brokerage business refers to the function of securities companies as securities agency business, providing securities agency business services for investors and collecting commissions.

A securities company is a company organization, including all the businesses that a securities company can do. Such as proprietary trading, investment banking, consulting services, asset restructuring and so on.