Retail orders generally trade with against market makers off-exchange, between the quoted market price. If the quote is Buy @ $1.00 x Sell @ $1.01, a retail ord

Retail orders generally trade with against market makers off-exchange, between the quoted market price. If the quote is Buy @ $1.00 x Sell @ $1.01, a retail order would be able to buy at a price like $1.0099. That $.0001 savings is known as "price improvement". Separately, the market maker pays a negotiated ahead of time rate to Robinhood for sourcing the order, aka "payment for order flow".