A hotel booking engine is an online application that facilitates direct hotel reservations through a hotel's website or social media, optimizing sales and simplifying the booking process. It integrates with property management systems to provide real-time data on room availability and rates, enhancing the customer experience. Key features to look for in a booking engine include customization options, mobile compatibility, and payment processing capabilities, with the Flightslogic engine offering comprehensive solutions for maximizing hotel revenue.