"Descriptive" marks are weak marks and are not inherently distinctive. Distinctive marks are protectable against infringement only if they have acquired "secondary meaning" such that the public associates the mark with the source of the goods and not as merely describing the goods themselves.  This allows the public to use the trademark terms in a descriptive manner.

"Generic" marks generically describe the goods themselves and are never entitled to protection.

An enforceable trademark must  be "distinctive," meaning that it must identify the source of a particular good.  Trademarks are rated by "strength" of the mark. 

"Arbitrary" and "fanciful" marks are strong marks.  They are inherently distinctive and are given a high degree of protection from infringement.  

"Suggestive" marks are also strong, inherently distinctive and given a high degree of protection from infringement.