Explanation:

An input or output is represented by a rectangle in flowchart symbols. The rectangle is a common symbol used in flowcharts to represent a process or operation. It is used to indicate that some action or task is being performed within the flowchart.

Flowchart Symbols:

Flowcharts use various symbols to represent different elements and actions within a process. These symbols help to illustrate the flow of information or activities in a clear and concise manner. Some commonly used symbols in flowcharts include:

- Oval: The oval shape represents the start or end point of the flowchart. It is used to indicate the beginning or end of a process.

- Square: The square shape represents a decision point or condition in the flowchart. It is used to indicate that a choice needs to be made or a condition needs to be evaluated.

- Rectangle: The rectangle shape represents a process or operation in the flowchart. It is used to indicate that some action or task is being performed within the flowchart.

- Parallelogram: The parallelogram shape represents input or output in the flowchart. It is used to indicate that data is being entered into the system or output is being generated from the system.

Input and Output in Flowcharts:

In flowcharts, input and output are represented by parallelograms. This is because input and output are external to the process and involve interaction with the user or external devices.

- Input: Input represents the data or information that is entered into the system or process. It can come from various sources such as the user, sensors, or other systems. In a flowchart, input is typically represented by a parallelogram shape.

- Output: Output represents the result or information that is generated by the system or process. It can be displayed to the user, stored in a database, or sent to other systems. In a flowchart, output is also represented by a parallelogram shape.

Conclusion:

In conclusion, the correct answer is option 'C' which states that an input or output is represented by a rectangle in flowchart symbols. The rectangle shape is commonly used to represent a process or operation within a flowchart. Input and output, on the other hand, are represented by parallelograms in flowcharts.