What's the difference between a broker and a liquidity provider?

Your broker sits between you and the market, and behind many brokers sit liquidity providers — banks and funds that supply the prices. Understanding one layer of this chain explains half of what you see in the terminal.

Post your questions:

• who sets the prices you see?
• why do different brokers show slightly different prices?
• what does "B-book" and "A-book" actually mean?

Plain-language answers only, please. This is a thread for clarity, not jargon.