It is the average of the last two-hundreds closing price on a specific time frame. One can plot the moving average 200 on any time frame. One does not have to calculate it because most charting software do have it.
Some trading software allow traders to plot MA 200 of the closing price, open price, midpoint, high and low. It does not matter because using the closing price does work fine. One can use the exponential or simple MA 200. Both work just fine.