What's the difference between dual-channel and single-channel mobile phones?

Single channel generally refers to the standby mode of the model with dual cards and dual standby.

Dual channel means that two mobile phone cards can stand by at the same time, and can send and receive text messages and answer calls at the same time.

Single channel means standby at the same time, but, for example, if you use one mobile phone card to surf the Internet and another mobile phone number to make a call, the card that is surfing the Internet will be disconnected/unable to send and receive text messages and make phone calls at the same time.