PortFast causes a switch or trunk port to enter the spanning tree forwarding state immediately, bypassing the listening and learning states.
You can use PortFast on switch or trunk ports that are connected to a single workstation, switch, or server to allow those devices to connect to the network immediately, instead of waiting for the port to transition from the listening and learning states to the forwarding state.
When the switch powers up, or when a device is connected to a port, the port enters the spanning tree listening state. When the Forward Delay timer expires, the port enters the learning state. When the Forward Delay timer expires a second time, the port is transitioned to the forwarding or blocking state.
When you enable PortFast on a switch or trunk port, the port is immediately transitioned to the spanning tree forwarding state.
To prevent loops from occurring in a network, the PortFast mode is supported only on nontrunking access ports because these ports typically do not transmit or receive BPDUs. The most secure implementation of PortFast is to enable it only on ports that connect end stations to switches. Because PortFast can be enabled on nontrunking ports connecting two switches, spanning tree loops can occur because BPDUs are still being transmitted and received on those ports.
Spanning-Tree Configuration guide:
When people talk about networks, they often refer to computers that are at the edge of the network as hosts, end stations, workstations, or servers. Its all just the same thing, a computer attached to the network; though the word HOST has the most general meaning and can include anything attached to the network including hubs, bridges, switches, routers, access points, firewalls, workstations, servers, mainframes, printers, scanners, copiers, fax machines and more.