A more thorough explanation:

A trademark class is a category used to protect a trademark for a specific type of product or service. There are 42 international trademark classes, with 34 classes for goods and 8 classes for services. Each class includes similar goods or services, and a trademark is protected in each relevant class.

• Class 25: Clothing, footwear, and headgear
• Class 35: Advertising and business services
• Class 42: Scientific and technological services

For example, if a company wants to trademark their clothing brand name, they would apply for protection in Class 25. If they also offer advertising services, they would need to apply for protection in Class 35 as well. By registering their trademark in the relevant classes, the company can protect their brand name from being used by competitors in those specific areas of business.