The term 'OFFICE NO.' can be broken down into three parts: TEL, EXT, and STE. TEL stands for telephone, which is a device used to make and receive calls. EXT stands for extension, which is a number that is added to the main telephone number of an office or organization. Finally, STE stands for station, which is a desk or work area in an office. Together, these three terms refer to the telephone number, extension, and station of an office.