A broker is an individual or a company who facilitates financial transaction execution on behalf of a trader. They basically act as sales agents.
There are mainly four types of broker in financial trading
Stock broker : Stock broker manages and executes the buying and selling of securities for the traders.
Forex broker :Forex brokers buy and sell currencies for the traders.
Full-service broker :Full-service brokers are financial advisers and offer more services for traders / investors ( on top of buying and selling ). Example tax advice, research, financial planning.
Discount broker : Discount brokers offer lower commission for executing the trades for the traders. The more trades you execute with them, the lower the cost.