For a trademark to be registrable, it needs to be “distinctive”. The purpose of trademarks is to “distinguish” one product from another product (or service). If the name is not capable of doing that, it cannot be protected and registered as a trademark.

A name is not distinctive if it:
– is a generic term of a product (“COOKIE” for cookie products)
– describes the products (“CRUMBLY” for cookies)
– is merely a laudatory term or expression (“SUPER” for any goods or services)

Distinctiveness is typically divided into five groups.

Generic names.  Generic names must be free for everybody to use in commerce so they cannot be protected with a trademark. It is possible to use generic names as product names, they just cannot be protected so everybody else is also allowed to use the same generic name. It is very difficult to build a brand on a generic term. Generic terms can be used effectively in distinguishing the company’s products from each other (e.g. Google Maps, Google Calendar, Google Analytics, etc.).
Blogger for a blogging platform

Descriptive names. These are names that describe some characteristic of a product or service, such as their quality, quantity, origin, characteristics, etc. Generally speaking, these cannot be protected, unless they are used to such extent that the “become” trademarks, i.e. the public starts identifying these are indicators of origin rather than descriptive terms So descriptive names can become protectable trademarks over time, but it is generally expensive to get them protected and there is a lot of uncertainty involved.
Sharp for televisions
DoubleClick for online advertising

Suggestive names. Suggestive names tell us indirectly something about a product and names can be protected as trademarks. For example, Greyhound and Jaguar are suggestive brand names for transportation services and cars. Both imply speed. Suggestive names work well as trademarks from both legal and marketing point of view. It often makes it easier to communicate a brand if there is some indirect connection to the product or service.
Greyhound for transportation services
Jaguar for cars

Arbitrary names. These are words and expressions that are taken out of context. Simply put, these are generic words but not in the field where they are being used as a trademark. These make good trademarks from legal point of view.
Apple for electronics
Camel for cigarettes

Fanciful/invented names. There are made-up words, like Pepsi or Kodak. These work well as trademarks and enjoy strong legal protection.
Kodak for photography equipment
Pepsi for beverages