ID is the abbreviation of English IDentity, which means identification number. It is called serial number and account number, which is a code and unique. Equivalent to an ID card. In a specific matter, its ID number is unchanged. As for what to use to identify that thing, it is determined by the rules formulated by the designer. This rule has certain subjectivity, such as employee job number, ID number, computer website, port number and so on.
SN is the serial number, which is the serial number. Sometimes it also refers to "machine code", which means that some software has taken certain protection measures to prevent piracy. When a user registers, a unique identification code will be generated according to the computer software and hardware information installed by the user's software, which is generally called machine code, also called serial number, authentication code, registration application code, etc.