Final answer:
A broker-dealer facilitates trading, an ATS matches orders electronically, and registered stock exchanges are regulated markets.
Step-by-step explanation:
A broker-dealer is a financial market entity that facilitates the buying and selling of securities on behalf of clients. They act as intermediaries between buyers and sellers and earn commissions on trades. An example of a broker-dealer is a full-service brokerage firm.
An Alternative Trading System (ATS) is a securities trading platform that matches buy and sell orders electronically. It operates outside of traditional stock exchanges and typically focuses on specific types of securities or trading strategies. An example of an ATS is the Electronic Communication Network (ECN).
A registered stock exchange is a regulated market where securities are traded. It has specific listing requirements for companies and operates under strict rules and regulations. Examples of registered stock exchanges include the New York Stock Exchange (NYSE) and the London Stock Exchange (LSE).