Trademarks are the brand names and symbols used by businesses to identify themselves and/or their products or services. The trademarks can be registered with the US government to prevent use by others. A trademark is considered intellectual property.
Some like Coca-Cola are very valuable, and have been used for over a century. Others like aspirin have become generic and are no longer trademarks.
To reduce the risk that a trademark might be declared generic, experts recommend that the trademark always be used as an adjective; never as a noun. Hence, "Kleenix tissues" is preferred over "Kleenix."