One concept you will frequently encounter as a Teenvestor is industry groupings. An industry represents a business category such as entertainment, real estate, banking, and so on.
Investors typically look at companies in the same industry in the same way.
For example, if the stock of Chase Manhattan Bank is doing really well, they'd expect other banks to do well also, otherwise they'd suspect something might be wrong with that bank. Industry categories are also important because they can help you decide which businesses are growing and which ones are dying. Before Gameboy, Nintendo, and other electronic games were sold to entertain people with time on their hands, there were pinball machines. While some adults may still play with pinball machines, young people today require more electronic gadgets for entertainment. An investment in a company that makes only pinball machines would not be wise because that segment of the entertainment industry is clearly not going to grow.