Moving Average is an indicator frequently used in technical analysis showing the average value of a security's price over a set period. It smoothes the price data to highlight long term trends or cycles. The fewer the data points in the MA the more short term or sensitive the trend will be.
The 50-day moving average is the security's average closing price over the last 50 days.
The 100-day moving average is the security's average closing price over the last 100 days.
The 200-day moving average is the security's average closing price over the last 200 days.
Prices higher than the Moving Averages are generally perceived as in a bullish trend and prices lower than Moving Averages are perceived as in a bearish trend.
The golden cross is a chart pattern created when a shorter term moving average was below a longer term moving average, but it crosses above that moving average. This is typically seen as a bullish signal. The golden cross is mostly used with longer term moving averages. It's an especially strong signal when the 50 day moving average crosses above the 200 day moving average.