A channel is a communication mechanism between your I/O driver and your process hardware. You define a channel by entering communication settings such as the network interface card (for an Ethernet driver) or the baud rate, parity, stop bits, data bits, and flow control values (for a serial driver) in your driver configuration program. The driver uses these settings to determine how to communicate with your process hardware.
Most of OPC drivers allow to configure multiple channels (paths) to your process hardware. This feature allows to set up different communication paths for hardware. For example, suppose your SCADA server has multiple network interface cards. You can configure one channel to use one interface card and the second channel to commuicate through a second card.