Rectangle symbol represents Input or Output in a flowchart.

Explanation:
A flowchart is a graphical representation of a process or system, which uses various symbols to represent different elements and their relationships. These symbols are connected by arrows to show the flow of the process.

The rectangle symbol in a flowchart represents Input or Output. It is used to depict the points where data is entered into the system or where data is produced or displayed as output. This can include reading data from a file, user input, displaying results on the screen, or printing information.

The rectangle symbol is typically labeled with a brief description of the input or output action. It can be placed at the beginning of the flowchart to indicate the initial input, or at various points throughout the flowchart to represent input or output actions that occur during the process.

Examples:

1. Input: In a flowchart representing a program that calculates the sum of two numbers, the rectangle symbol can be used to represent the input action of entering the two numbers.

2. Output: In a flowchart representing a program that displays the result of a calculation, the rectangle symbol can be used to represent the output action of displaying the result on the screen.

In both cases, the rectangle symbol represents the point where data is either entered into the system or produced as output.

Overall, the rectangle symbol in a flowchart represents Input or Output, indicating the points where data enters or exits the system. It is an essential element for accurately representing the flow of a process or system in a graphical form.