A trademark is a word, name, symbol or device that identifies and distinguishes the source of consumer goods and/or services.
It might be helpful to discuss what a trademark is NOT rather than what it is, because it can be easy to confuse the different types of intellectual property. There are copyrights, patents, and trademarks. Copyrights are for protection of creative expressions, such as songs, movies, photographs, novels or poems. Patents are for protecting rights in functional and useful inventions.
Trademarks are different, because trademark law originates from consumer law. Its primary original purpose was to prevent counterfeiting, but now its main function is to prevent confusion among consumers. While trademarks do offer benefits to the trademark owner, the law is shaped around preventing consumers from being confused. If you wanted to start a beverage company, you could not call it Coca-Cola, because that would confuse consumers into thinking that your product had an affiliation with Coke.
Trademarks can be words or symbols or a combination of both. In the Nike trademark, there are at least three distinct trademarks. The word “Nike” is a registered trademark for lots of things. The “swoosh” logo is also a registered trademark. And the combination of the two together, with the recognizable writing of the word “Nike” is also a trademark. These symbols are easily recognizable by almost everyone as the source of shoes, t-shirts, golf clubs, software applications, and much more. The same is true with the Netflix logo and many other source identifiers.
To have a trademark you must be using your mark in commerce. You receive more protection once the trademark is registered, but there is no legal requirement that you register your trademark. However, if you do register your trademark, you receive benefits that unregistered trademarks cannot claim, such as increased damages, a presumption of your ownership and the validity of the trademark, the ability to list your trademark with the US Customs and Border Patrol to prevent importation of counterfeit goods.