Moving Average
Moving Average is calculated by averaging the price for a given number of days backwards.

There exist many types of moving averages, for example simple “moving average”, “exponential moving average”, and others. The difference is mainly the weighting of the days, some treats all days as equal in the calculation, other weight the nearest days back more than the days further in the past.

Moving average is used to be drawn with different timeframes, some common are the 50-day moving average, and the 200-day moving average. The longer time frame the smoother the curve will go, and the longer trends it will show. It can also be applied to intraday charts, with minutes instead of days.

Trading with Moving Average.
(Note, I am skeptical to this.)
The belief by the Technical Analysis people are that when the price closes above a given moving average, it gives a buy signal, when it closes below it gives a sell signal. The crossing of the line signals a change in trend.

Two Moving Averages can be used to determine buy and sell signals. For example a slow line with a 200-day Moving Average and a faster line with a 50-day Moving Average. When the fast line crosses the slow line a signal is given. If the MA-50 is crossing from below the MA-200 to above a buy signal is given, a sell signal is given when MA-50 crosses from above to below the MA-200 line.

The critique of the Moving Average method.
The Moving Average method is for capturing and holding a stock while it continually goes higher (it is in an upward trend), and sell it when it stops to go higher. When you look at stock charts, you can see that following the moving average method in fact would have made you money sometimes. But when examining a lot of charts you will see that the method also will give you a fair amount of false signals, that you will not make any money on, or loose money. Sometimes the market “trends” a long while, other times it will go up and down in small changes. All the losses when the market does not trend and trading commission will eat heavily into the possible profits. The question if it will trend this time may be looked on as a coin flip.

Bottom line:
The serious long term investor do not need Technical Analysis