Final answer:
The diamond shape, known as the decision symbol, is used in flowcharts to represent a Boolean expression where a decision based on a yes/no question is made.
Step-by-step explanation:
In flowcharting, the symbol used to represent a Boolean expression is typically the diamond shape, which is known as the decision symbol. It's used to depict a point where the flowchart needs to make a choice, based on a yes or no question, which is essentially a Boolean value. As an example, when deciding if a number is even, a flowchart might have a diamond-shaped symbol with a Boolean expression like "Is the number even?" that leads to two branches: Yes (true) or No (false).