Extension: Securities is the abbreviation of "marketable securities", which is the general name of various economic rights and interests certificates. Marketable securities are a kind of valuable documents that express property rights, and holders can prove their ownership or private rights such as bonds based on the documents. Mainly including capital security, currency securities and commodity securities. In a narrow sense, securities mainly refer to securities products in the securities market, including property market products such as stocks, debt market products such as bonds, and derivative market products such as stock futures, options, interest rate futures and options. The subject system of securities science is an organic system composed of various branches that study the behavior characteristics and operating rules of the securities market from different angles, mainly including two research fields: traditional securities theory and evolutionary securities theory.