A channel manager is a software product that connects a hospitality accommodations provider (eg: hotel or vacation rental) to online travel agencies and distribution channels to generate demand for the property.
The software helps send rates, inventory, and availability to OTAs using APIs from a common user interface and gets bookings / reservations from all online channels into a common easy to view and use platform.
This ensures that the hotel does not need to manage each OTA individually by pooling all data into a common system, and hence ensuring there are no overbookings or rate disparity.