The symbol "ℂ" represents the set of complex numbers in mathematics. Complex numbers are numbers that have a real part and an imaginary part, typically expressed in the form a + bi, where "a" is the real part, "b" is the imaginary part, and "i" is the imaginary unit defined as the square root of -1. This set is essential in various fields, including engineering, physics, and applied mathematics. Complex numbers allow for the solution of equations that do not have real solutions, such as x² + 1 = 0. The introduction of complex numbers expands the number system beyond the real numbers, denoted by "ℝ," enabling mathematicians to explore new concepts and solve problems in a more comprehensive way.