Direct Connect is a synonym of Interface. A point where two systems or organisations, meet and interact.
In the tourism/hospitality industry Direct Connect is a technological connection that interchanges and synchronises data across multiple distribution channels, such as between a Hotel CRS (or PMS) and OTAs.
A commonly used standard interface is the so called XML, which enables real-time, two-way communication link between a hotels reservation system and a third party (for direct rate and availability updates). It means that the OTA reservations are then automatically sent to the hotel via the CRS / PMS.
The advantage of direct links is reduced maintenance for rates and availabilities. Meaning reduced workload and minimisation of human mistakes.