A bridge is a network function that connects multiple network interfaces so they can operate as part of the same local network.
In a MikroTik setup, a bridge can group Ethernet ports or other interfaces together, allowing connected devices to communicate through the same Layer 2 network. The Centipid discussion specifically refers to adding ports to a bridge and using the correct bridge or interface when connecting a MikroTik router.
Related terms: Bridge Interface, Bridge Mode, Ethernet Port, LAN, WAN, Interface, MikroTik, VLAN