Virtual properties are a feature in programming, particularly in object-oriented languages like C# and Java. They allow developers to define properties that do not store data directly but instead compute their values dynamically when accessed. This means that the value of a virtual property can change based on other data or conditions, providing flexibility and efficiency in code. For example, a virtual property might calculate a person's age based on their birthdate rather than storing the age as a separate value. This ensures that the age is always accurate and up-to-date without needing to manually update it whenever the person's birthday occurs.