Trademark Offices around the world use classes to divide commercial products and services into defined categories.  When you apply for your trademark to protect your brand, you must define the class or classes that you believe are best describe your business activity. 

There are 45 classes – 34 for products and 11 for services – which countries from around the world have standardized for international use under the "Nice International Classification".

These classes group all known products and services. You can register the same trademark if there are similar classes, for example, you may register the trademark KING for computers in class 23, and you can also register the same trademark in class 24 for cosmetics. 

Trademark protection only extends to commercial use within your specified classes.  It is possible, then for two entities conducting business in different classes to use the identical or similar trademarks and for each entity to enjoy full trademark protection in their respective classes. You can choose multiple classes under which to conduct business if you feel the protection must extend beyond only one class.

You can perform a search of your class with the following tool Trademark Class Search