A mark is only protected in connection with the goods or services for which it is used. That is why, for example, the DELTA mark can be used without confusion by different companies for airline services, faucets, and more.
"Goods" are products, generally physical items like chemicals or hair dryers or wheat. "Services" are services provided to others, such as chemistry research services, hair salon services, or restaurant services.
For the purposes of clearing a mark, like a clearance search using TrademarkClear.com, it is important to identify the products and services that you plan to use your mark on. For example, you might plan to use the mark "Three Blind Mice" (the mark) for "hockey sticks" (the products).
As a result, picking the proper goods or services at the time you file a trademark application is key. The descriptions of goods or services cannot be expanded after filing – the only way to cover additional goods and services is to file an additional application.
However, the application cannot be too broad, either. At the time of filing, an applicant filing a trademark application at the US Patent & Trademark Office must file a sworn declaration for each class of goods or services attesting either that: (a) the applicant has a bona fide intent to use the mark in interstate commerce for the listed goods and services in that application (or in that class) or (b) the applicant is already using the mark for all listed goods and services in the application (or in that class).
After filing, the descriptions of goods or services can be amended to clarify the nature of the goods or services, to conform to USPTO expectations about descriptions of goods or services, or may be moved from one international class to another class. For more information about international classes, please read our guide "What Is an International Class In a Trademark Application?" If the net impact is to add an international class or classes to the total number of classes already in the application, and additional fee may be due.
While international classes are a convenient way to group similar goods and services, not all goods and services in the same class are similar (e.g. accounting software and scuba apparatus, both in Class 9), and not all goods and services in different classes are unrelated (e.g. workout shorts in Class 25 and clothing retail service in Class 35).