Tri-state
Tri-state is a term used in digital electronics to describe a third state of a signal line, in addition to the two traditional binary states (0 and 1). The tri-state state is also known as high impedance or open state.

Output Port
An output port is a hardware interface on a computer or electronic device that is used to send data to an external device or another computer system. It allows the computer to communicate with external devices or systems by transmitting data signals.

Input Port
An input port is a hardware interface on a computer or electronic device that is used to receive data from an external device or another computer system. It allows the computer to accept data signals from external sources.

Parallel Port
A parallel port is a type of interface found on computers that enables data to be transferred in parallel. It is typically used to connect devices such as printers and scanners to the computer. Parallel ports can transfer multiple bits of data simultaneously, making them faster than serial ports.

Output-Input Port
An output-input port is not a commonly used term in digital electronics. It may refer to a port that can function as both an input and output port, allowing data to be both sent and received.

Explanation
The correct answer is option 'A', output port. Tri-state is often associated with output ports because they can be configured to have a third state, which is high impedance or open. In this state, the output port does not drive any voltage or current onto the connected circuit, effectively disconnecting itself from the external devices. This allows multiple devices to share the same bus or line without interfering with each other.

By using tri-state output ports, devices can be connected together in a bus architecture, where each device can drive the bus with its output port when necessary, and then tri-state the bus when it is not actively transmitting data. This helps to prevent conflicts or contention on the bus.

Tri-state output ports are commonly used in scenarios where multiple devices need to share a common communication line or bus, such as in microcontrollers, memory chips, and digital buses like I2C or SPI.

In summary, the tri-state is a third state of a signal line, and it is often associated with output ports in digital electronics. Output ports can be configured to have a high impedance state, which allows multiple devices to share a common bus or line without interference.