Periodogram

A periodogram is like a graph that tells you if your data has repeating patterns in it. It shows the strength of each repeating pattern, which is also called frequency. The higher the frequency, the bigger the pattern is.
The graph has an x and a y axis. The x axis shows the frequency and the y axis shows the strength of each pattern. If the graph has a high peak, that means the pattern is strong and it's repeating a lot.