More and more you see derivative (futures) contract called perpetual.
Meaning there is no expiration date so, in practice, you can trade them long term.

However a common practice is to trade these contracts on a daily or weekly basis because of the Interest you pay by holding them.

It is better to carefully learn and understand how the contracts work as they differ from an exchange to another and can quickly turn out complicated.

BitMex is giving some documentation about their own perpetuals: