Which of the following describes a floating-point number?

A floating-point number is indeed described as an approximation of a real number using significant digits. This representation allows for a much larger range of values compared to integers by including both whole numbers and fractions. Floating-point numbers are particularly useful in scientific calculations that require precision and the ability to represent very small or very large numbers, which integer types cannot accommodate.

In Java programming, floating-point numbers are represented using the float and double data types, both of which can store real numbers with decimal points. However, due to the way they are stored in memory, floating-point numbers do not always represent real numbers precisely, leading to potential rounding errors. This characteristic of using significant digits enables floating-point numbers to approximate a wide range of real values, which is essential in various applications like simulations, graphics, and complex mathematical calculations.

The other choices each represent different concepts that do not align with the definition of floating-point numbers, making the chosen option the accurate representation of what a floating-point number is.