Relative Strength is a measure of price growth that indicates how a stock performs relative to the rest of the market. It is a numerical measurement expressed as a percentage. For example, if a stock has a relative strength of 90, it has outperformed 90% of the stocks over a specified period. The Relative Strength is calculated against all stocks of the exchange that a stock is listed on. That is, the "rest of the market" here is the exchange. So, for example, it's NYSE for "Alcoa" and Nasdaq for "Apple". Be careful not to confuse Relative Strength with the Relative Strength Index.
