Is that a source identifier in your pocket or are you just being descriptive?
A trademark gives its owner an exclusive right to use it in connection with a particular kind or category of products or services. At the same time, though, trademark law seeks to promote competition. To that end, it generally does not allow people or companies to claim the exclusive right to use generic words or words that are used to describe a feature or quality of a product. If someone could claim an exclusive right to use gasoline or unleaded as a trademark for petroleum products, then nobody else could enter the market.
To qualify for trademark protection, a mark cannot be merely descriptive of the product or service. It must be distinctive, in the sense that consumers see it not merely as a description of the product or service but as an identifier of the source of the product or service, that is to say, an identifier of the producer or sponsor of the product or service.
Sometimes a mark that is merely descriptive at first acquires distinctiveness over time. Through advertising and long usage, consumers come to see it as a source-identifier. International Business Machines (IBM) is an example. It is descriptive of the product or service, but over time consumers have come to associate it with a particular source of business machines. In general, though, words and phrases that are merely descriptive do not qualify for trademark protection.
Inherently Distinctive Trademarks
Some kinds of marks are regarded as inherently distinctive, meaning there is no need to make a showing of acquired distinctiveness before trademark rights may be claimed in them. A mark is inherently distinctive if it is fanciful, arbitrary, or suggestive.
A fanciful mark is something that is completely made up. Xerox is an example.
An arbitrary mark is one which, although a real word, bears no logical relationship to the product or service. Apple, as a trademark for computers, is an example.
A suggestive mark is one that hints at but does not directly describe a quality or feature of a product or service.
Why It Matters
A lot rides on whether a mark is suggestive or merely descriptive. If it is merely descriptive, then its first use in commerce will not be as a trademark. Competitors may freely use the same mark until it acquires distinctiveness. If you try to register it with the USPTO, you might get it on the Supplemental Register, but it won’t make it onto the Principal Register. It will not enjoy the presumptions of validity and ownership that trademarks registered on the Principal Register do. Maybe you will be able to get it there someday, but only if you present persuasive evidence of acquired distinctiveness.
Suggestive trademarks, on the other hand, may qualify for trademark protection upon their first use in commerce. And if registered, they get all the advantages of being included in the Principal Register.
Where Is the Line?
The difference between descriptiveness and suggestiveness is not very intuitive. The classic formulation is that a descriptive term directly describes something, while a suggestive term merely hints at it. If a term directly states what a product or service is or does, or literally describes a feature or quality, then it might be generic or descriptive, but it is not suggestive. If a term does not directly describe the product or service, or a quality or feature of it, that is to say, if some additional thought process is needed to get to the intended description, then it is suggestive.
Jaguar is an example of a suggestive trademark. The product does not literally feature or contain a wild animal. An additional thought process is needed to get to the intended descriptor, which in this case would be fast. Fast would be a merely descriptive mark for a car. Jaguar requires an additional thought process, namely, the idea that jaguars are fast, to reach the intended meaning.
Coppertone is another example. Suntan oil would be a descriptive mark. Coppertone, on the other hand, does not directly describe the product. Instead, it suggests what might happen if someone uses it, i.e., the person may acquire something akin to a copper skin color.
Incidentally, changing the spelling of a descriptive term generally will not bring it into the realm of inherent distinctiveness even if the word, as so spelled, technically is an invented one. Fastt Car, for instance, would almost certainly be treated by the USPTO or a court as a merely descriptive trademark. The relevant question is whether consumers would read or hear it as an adjective, not whether a member of the Spelling and Grammar Police Squad would.
Criticism
Courts and legal scholars have noted that the line between descriptiveness and suggestiveness is not always clear. Professor Jake Linford, for example, has argued that the distinction is “illusory at best,” and that a suggestive mark is “more like a descriptive mark than the law currently recognizes.” (Jake Linford, The False Dichotomy Between Suggestive and Descriptive Trademarks, 76 OHIO ST. L.J. 1367 (2015), available here. )
Nevertheless, the distinction is currently recognized in the law, at least in the United States.
European Union
The European Union appears to take a narrower view of suggestiveness. For example, it denied protection for “How Can I Make You Smile Today?” as a trademark for orthodontic and dental supplies. As certain fast food chains and performing artists can attest, slogans and phrases can easily be claimed as trademarks in the United States. This slogan would clearly fall on the “suggestive” side of the suggestive/descriptive line under the classic formulations of the distinction in the United States.