This is the send value for clients that do not match any entry in the access-list. 

The option "Default Forward” in the wireless card configuration of a MikroTik router refers to the ability to forward traffic between clients connected to the same wireless network. When this option is enabled, it allows devices connected to the MikroTik router's Wi-Fi access point to communicate with each other.

This is crucial for applications that require device-to-device communication within the same network, such as file sharing, playing network games, or any other application that requires devices to “see” each other on the same local network (LAN). .

On the contrary, if you disable the “Default Forward” option, you are effectively isolating the connected devices on the wireless network, so that they cannot communicate directly with each other.

This setting can be useful in environments where security is a big concern, such as on public Wi-Fi networks or in cafes, where you don't want client devices to be able to try to access or communicate with each other. This isolation helps protect against attacks from one device to another within the same wireless network.

In short, “Default Forward” controls whether wireless clients on the same network can communicate with each other. Enabling it allows communication between devices, while disabling it provides an additional layer of security by preventing this direct communication.