As far as futures are concerned, there are two operations: buying or selling. Generally speaking, buying is called more, selling is called empty. It is clear to understand these two operations.

As for short selling, strictly speaking, this is option theory, short selling. This is because options are divided into call options and put options. You can understand that call options are long, put options are short, and options can be buyers and sellers, such as buying put options or selling put options. The former generally sells short, while the latter sells short (short selling is actually long).