In desktop virtualization, a connection broker is a software program that allows the end-user to connect to an available desktop. 

The connection broker performs tasks that include:

• Validating the user name and providing a connection for the user.
• Providing the ability for the user to connect to a specific virtual machine (VM), virtual client, PC blade or terminal services server.
• Providing the ability for the user to access multiple VM pools. (If the user is permitted to access a variety of pools, the broker prompts the user to select a pool at login time.)
• Monitoring the activity level of a given virtual machine and setting status to active or inactive.
• Handling reassignment of a virtual machine when a user disconnects.

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VDI on VMware infrastructures: The role of the connection broker