Class:

Abbreviation for the International Classification of Goods.  The United States is a contracting party to the Nice Agreement (a treaty among over 75 countries), which enables universal classification of registered trademarks and service marks.  For example, if you were to register a mark for clothing, the International Classification for such goods is Class 25.  This classification is identified by the same number in the other countries that are signatories to the Nice Agreement.

 

Office Action:

A communication from the USPTO regarding the applicant's trademark application.

 

Trademark:

A word, name, symbol or device which is used in trade with goods to indicate the source of the goods and to distinguish them from the goods of others.  A servicemark is the same as a trademark except that it identifies and distinguishes the source of a service rather than a product.  The term "trademark" and "mark" are commonly used to refer to both trademarks and servicemarks. 

Trademark rights may be used to prevent others from using a confusingly similar mark, but not to prevent others from making the same goods or from selling the same goods or services under a clearly different mark.

  

USPTO:

The United States Patent and Trademark Office, which is the governmental body that administers trademarks.