An arbitrary mark is a business or product name that is totally made up. Arbitrary marks are not only creative and fun, but quite easy to get registered, since a likelihood of confusion is near impossible. Suggestive marks have a greater connection to the products and businesses they represent. Note, however, that the mark does not fully describe the product in question. Suggestive marks, like arbitrary ones, tend to register without many problems.
Descriptive marks are more complicated.
If the government were to grant you the sole right to use descriptive words in promoting products or services, it may be unfair to competitors who also need the words to effectively market their goods. This means that you have used the mark long enough and widely enough for a substantial amount of people to think of your business upon seeing or hearing the mark. A generic mark either always was, or has recently become the primary way that people describe the basic product represented. Generic marks are rarely entitled to registration, as the Trademark Office considers it unfair to prevent competitors from using certain words that are necessary to promote their goods or services. We take pride in saving unnecessary registration fees when the mark in question is unlikely to register from the beginning.