In the general field of securities analysis (predicting stock prices) there are two basic schools of thought, fundamental analysis and technical analysis. Fundamental analysis can be summarized as saying that stocks are worth a price based on their financial statements and that investors can profit by deeply understanding the details of said information. Benjamin Graham with his book “Securities Analysis” is an example of a fundamental approach to stock valuation.
On the other hand, a different school of thought belongs to the technical analysis camp, which states that stock prices have patterns and can be bought or sold for profit based on these patterns. Technical analysts frequently chart stocks and are responsible for the myriad types of charts available at any financial web site (such as Yahoo!) including “Bollinger Bands” and the like.
Without going into the relative validity of both theories (an endless topic in and of itself) I will glibly summarize the two models as “buy it because your detailed financial analysis says it will go up in value” vs. “buy it because it has been going up and other items similar to it are going up in price”.