When you apply for registration of your Trademark, you apply to register it under the class of goods or services your Trademark will cover.
Under the NICE International Classification (an international Trademark classification system), there are 45 classes (35 classes for goods and 10 classes for service). Each Trademark application is for a single class only, though you may include more than one good or service under the same class in one Trademark application (but not the entire class).