Cisco FlexStack-Network stacking module-expansion slot
A single FlexStack connection between two members is a full duplex 10Gbps connecton. Each Cisco Catalyst 2960-S member supports two FlexStack connections. Each FlexStack member can simultaneously send and receive Ethernet traffic over both stack links at line rate, effectively giving 20Gbps of stack bandwidth per member.
Up to four switches can stacked together using FlexStack to form a single logical switch. Logical switch is another term used to identify a stack of switches. There are multiple physical switches acting as a single unit. This single unit behavior is a logical switch.