The first category to consider is generic trademarks. Suppose a consumer is selling candy bars, and wants his trademark to be CANDY BARS. This won’t be acceptable as a trademark because CANDY BARS is just the commonly understood name of what the consumer is selling.
The reason generic trademarks can never be registered has to do with the purpose of trademarks. We register trademarks to prevent other companies from profiting off of your hard-earned brand. It wouldn’t make sense to allow people to register for generic trademarks because everyone in the candy bar industry needs to be able to use words, like candy bars, in advertising materials.
The second category is descriptive trademarks. Descriptive trademarks describe an ingredient, quality, characteristic, function, feature, purpose, or use of what a consumer is selling. Suppose a consumer is selling candy bars, and wants her trademark to be SUGAR. This would be a descriptive mark, because sugar is an ingredient in candy bars.
These are unlikely to get registered on the Principal Register because they merely describe what that consumer is selling.
The third category is suggestive trademarks. Suggestive marks hint at what you’re selling, but doesn’t actually describe what you’re selling.
Another way to think of this is the trademark takes some imagination for consumers to understand what you’re selling. An example of a suggestive trademark for candy is ALMOND JOY. These words hint at what you might be selling, like candy bars, but it takes some imagination to get there.
The fourth category is arbitrary trademarks. This is a trademark that may have a common understanding for another product or service, but doesn’t relate to what you’re selling.
An example of an arbitrary mark is BOAT for selling candy bars. BOAT would be generic if you’re selling boats, but has no meaning in relation to candy bars.
And finally, the fifth category is fanciful trademarks. The best way to think about these trademarks is that they have no meaning. An example of this would be KAMAKI for chocolate bars. Since KAMAKI is a made-up word and has no meaning in any language, it is considered fanciful. And, because fanciful trademarks are so unique, they are entitled to the strongest level of protection against possible infringers. Once you know what kind of trademark you need for your brand, the next step is to register it.