"Functional Equation - Part 1" by Pang-Cheng, Wu introduces the concept of functional equations, which are equations involving unknown functions rather than unknown numbers. The document focuses on basic concepts, examples, and methods for solving these equations, particularly within the context of Olympiad Algebra. It explores techniques like substitution, injectivity, surjectivity, and establishing inequalities, and it also covers Cauchy's functional equation and methods for solving equations over different domains like real numbers, integers, and polynomials.