There is no such thing as “singlemode” or “multimode” in the firewall. Those are traditionally used to refer to fiber media types. Single context mode and multi context mode are explained here:
You can partition a single ASA into multiple virtual devices, known as security contexts. Each context acts as an independent device, with its own security policy, interfaces, and administrators. Multiple contexts are similar to having multiple standalone devices.
Multi context - is a great feature available for all current firewalls. to explain it takes time but in short i say -- multi context is used to split physical firewall into multiple virtual firewalls and assign rules based on context, this is mainly used in Service providers environment.
below i would provide links that has detailed information !!!
