1. The problem asks: What is the period of a function? 2. The period of a function is defined as the length on the x-axis of one complete cycle of the function. 3. This means the period measures how long it takes for the function to repeat its pattern along the x-axis. 4. Other options like "how high and low the function goes from the center line" describe amplitude, not period. 5. The range of the function refers to the set of all possible output values, not the period. 6. The height of the function is related to amplitude or maximum value, not period. 7. Therefore, the correct definition of the period is: the length on the x-axis of one cycle. Final answer: The period of a function is the length on the x-axis of one cycle.