Technical Analysis (TA) is a commonly used method of evaluating stock by examining statistics of market activity, such as previous volume and/or prices. This typically doesn't try to measure a stock's intrinsic value, but rather to use charts and tools to identify patterns, which can often times be used for predictions on the stock's future activity.
TA is an extremely effective tool when used correctly. There are many naysayers with regard to this style of analysis, but that does not change the fact that it works. TA will not result in a successful trade every time, but a skilled technical analyst can greatly improve their probability of success on any given trade by using TA.
Some Trader's use TA exclusively, some use a combination of technicals and fundamentals, and some solely use fundamentals. It all depends on where your strengths lie as a Trader.
Technical Analysis is commonly used in stock trading, futures trading, options trading, and almost exclusively when day trading. Commonly used technical analysis patterns are: island reversal, percent price oscillator, Fibonacci measurements, and relative strength index