Complex Number: A complex number is a number that can be expressed in the form $a + bi$, where $a$ and $b$ are real numbers, and $i$ is the imaginary unit, defined as $i^2 = -1$.
Imaginary Unit:The imaginary unit, denoted as $i$, is a mathematical construct that satisfies the equation $i^2 = -1$. It is used to represent the square root of a negative number.
Real Number: A real number is a number that can be expressed on the number line, including positive and negative integers, fractions, and irrational numbers. Real numbers do not include imaginary numbers.