A trademark is a unique way of identifying a company or an individual. This is done through a word, a symbol, a phrase or even a device. A trademark is unique enough that any person can easily identify it. For example, Coca Cola's unique bottle shape stands out from the shape of other soda bottles. The same goes for the distinctive red logo that is unique to the brand and is different from other soda brands. When you see the unique shape of its bottle or just the logo, you will immediately know that the product is Coca Cola and not another soda.
A trademark manages to be unique to each other because it is registered with the United States Patent and Trademark Office. By registering the trademark with the USPTO, no other company can make a trademark that is similar to a registered trademark. A trademark acts like a copyright in the sense that the first one who is able to register their brand gets the “first rights.” It is also different from patents in that there is no such thing as a “trademark pending.”
A trademark can be so associated with a particular product that at some point the trademark becomes the generic description of that product. When people buy cotton swabs you'll usually hear them look for Q-tips. The name Q-Tip is actually a brand of Johnson and Johnson, but because of familiarity, it has become a generic name for all cotton swabs. Other brands that have become universally accepted include Jacuzzi, Crayola and Band-Aid.