The graph below shows the 1458 daily simple moving average (1458d SMA). A simple moving average takes the average of all the prices in a list.

As an example, let's take the 3 day moving average for the following prices: 250, 320, 280. The daily moving average would be: (250 + 320 + 280) / 3 = 283.33

Similarly, the 1458d SMA will take the daily closing prices of the last 1458 days and return the average.