The average price over a specific period. EMA (Exponential) reacts faster to recent price changes.
Example
A common signal is the 'Golden Cross': the 50-day average crosses above the 200-day average — historically often the start of longer uptrends. Conversely, the 'Death Cross' (50 below 200) warns of weakness. The EMA reacts faster than the simple MA because it weights recent prices more heavily. Many traders also use the EMA20 or EMA50 as dynamic support within a trend.