A poker room rate is a discount offered on hotel room rates to players who agree to play a certain number of hours of poker in the poker room of the hotel. A poker room rate is a common feature of casino/hotels in Las Vegas, and occasionally is found at hotels in other cities.
The details of the offer vary from hotel to hotel. Clearly, a casino must have an attached or associated hotel in order to offer a discount. Discounts can range from minimal ($10 off per room or so) to large (20% or more), and the number of hours required to play also varies from casino to casino.
For example, at the Excalibur, a player who wishes to earn a poker room rate simply checks in with the brush whenever they enter or leave the room, and if the player plays at least five hours a day in the Excalibur poker room, they get a discounted rate on their Excalibur room that amounts to around $25 off per night. Other properties have other requirements and other discounts.
For a relatively up-to-date listing of casinos in Vegas and their current poker room rates, you can visit the Poker Room Rate Page at All Vegas Poker. Though, as that page advises, always call ahead to the poker room and ask, to make sure you have the most recent details about their offers.