This one-page reference sheet covers the key concepts of mathematical functions, including definitions of domain and range, function notation, identifying functions from tables and graphs, and an introduction to linear and nonlinear functions. Students can use it to review the relationship between inputs and outputs, vertical line test, and how functions are represented in multiple ways. The sheet serves as a concise study resource during instruction, independent practice, or test review. It is designed to support learners across pre-algebra through early algebra courses.