Which of the following is not a valid data type?

The choice indicating that "Start date" is not a valid data type is correct because in most contexts, particularly in programming and data analysis, dates are typically represented using a date data type or a timestamp, not specifically termed "Start date."

In data analysis and database management, standard valid data types include text (used for strings of characters), numbers (which can represent integers or decimals), and Boolean (used for true/false values). While "Start date" may conceptually describe a specific usage for date data—like indicating the starting point of a timetable—it isn't recognized as a fundamental or distinct data type in the same way the other options are.

Understanding the differing terminology and definitions for data types is essential within data management practices, as it ensures accurate data handling and application development.