Definition of stamp collecting: (Huang Xianghui's Basic Stamp Collecting)
Copy: refers to the smallest unit that can not be separated by tearing or cutting from a whole stamp or a whole tube, and has the function of independent use.
Zhang: refers to the smallest unit of measurement in the printing process of stamps (except roll stamps and small promissory notes) before the finished products leave the factory. It can be divided into printed bills and post office bills. Printing the whole page refers to all stamps printed on the same printing plate after printing is completed; Post office stamps refer to the whole stamps that are printed, inspected and packaged, and the finished products are distributed to post offices for sale.
The whole post office is usually called "version".