Technical Analysis involves looking at charts of prices to get a better understanding of where prices have been, where they are, and ultimately where they are headed.
Just as a meteorologist studies charts of weather patterns (e.g., the jet stream, satellite photos, pressure systems, etc.) to anticipate changes in the weather, technicians use charts (and technical indicators) of security prices to anticipate changes in prices.
Technical analysis focuses on the well defined principles of supply and demand. This makes it well suited to investing in stocks, bonds, options, commodities, futures, indices, mutual funds--anything that has a large supply of buyers and sellers.