To understand perpetual trading, we must first grasp the concept of derivatives. A derivative is a financial instrument whose value is derived from an underlying asset, in this case, a cryptocurrency.
In traditional derivative products such as futures contracts, each contract has an expiration date. On the other hand, perpetual trading is a contract with no expiration date. This means that traders can hold long or short positions for as long as they desire.
Please refer to this link for a more in-depth explanation of perpetual trading.