Channel
A channel is a conduit to I/O services covering such items as files, sockets, hardware devices, I/O ports or some software component.
Channels are open upon creation, and can be closed explicitly. Once a channel is closed it cannot be re-opened, and any attempts to perform I/O operations on the closed channel result in a ClosedChannelException.
Particular implementations or sub-interfaces of Channel dictate whether they are thread-safe or not.