Classification number and main classification number are mainly for patent purposes. If a patent has two or more uses, the examiner will give multiple classification numbers corresponding to its uses. The classification of the main purpose is called the main classification number, and the classification number of the secondary purpose is called the secondary classification number.
International patent classification is a general international patent literature classification. The classification number obtained by classifying patent documents with the international patent classification table is called the international patent classification number, which is usually abbreviated as IPC.