Relative Strenght Index [RSI]
There are a few definitions of RSI, but the most used are:
"The Relative Strength measured by looking at daily positive and negative changes"
In more human term you can say that RSI measures if a stock is oversold, overbought or just somewhere in the middle. It is done by looking at how many days a stock has been rising or falling in a period of time. If a stock has been gaining to long there is a far chance it will take a break. To visualize the increased risk our charts are colored with a red line. The line does not mean that you must sell, but to watch it even closer. Some stocks go very high while being overbought on RSI like the stock shown below. Oversold is colored with green colors. RSI is often done for 14 or 21 days depending on charting period.