Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on broadcasting to locate unknown devices. Once a device has been located, its location is recorded in some fashion so as to preclude the need for further broadcasting. A network switch (or just switch) is a networking device that performs transparent bridging (connection of multiple network segments with forwarding based on MAC addresses) at up to the speed of the hardware. There are four forwarding methods a switch can use: * Store and forward - The switch buffers and, typically, performs a checksum on each frame before forwarding it on. * Cut through - The switch only reads up to the frame's hardware address before starting to forward it. There is no error checking with this method. * Fragment free - A method which attempts to retain the benefits of both "Store and Forward" and "Cut-through". Fragment Free checks the first 64 bytes of the frame, where addressing information is stored. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device in Layer 3 or Layer 4 (OSI), typically a router. * Adaptive switching - A method of automatically switching between the other three modes. Note that "cut through" switches have to fall back to "store and forward" if the outgoing port is busy at the time the packet arrives. Note that these forwarding methods are not controlled by the user and are configured only by the switch itself. An Ethernet hub or concentrator is a device for connecting multiple twisted pair or fiber optic Ethernet devices together, making them act as a single segment. Hubs work at the physical layer (layer 1) of the OSI model. The device is thus a form of multiport repeater. Ethernet hubs are also responsible for forwarding a jam signal to all ports if it detects a collision. A router is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as routing. Routing occurs at layer 3 (the Network layer e.g. IP) of the OSI seven-layer protocol stack. A router acts as a junction between two or more networks to transfer data packets among them. A router is different from a switch. A switch connects devices to form a Local area network (LAN) (which might, in turn, be connected to another network via a router).

I'm going to answer this in the context of a home user, not give you verbatim definitions, which you could easily find online. First, a hub is simply a box that allows for the connection of multiple computers. It's the device that made it possible for us to use Cat 5 twisted pair cabling to connect our computers together without having to run a coax cable from one computer to another in a big long bus. A hub does not inspect the network traffic, it simply passes every packet along from whatever port it came from to every port. In times of high traffic, this causes collisions. Network hubs are rare now for home use, because the more sophisticated devices are more efficient and practical, as you will see. Second, a switch is a like a hub that inspects traffic to see where it came from and where it's headed, by physical address (MAC address). Every network adapter would have a different MAC address. A switch (also known as a transparent bridge) only sends packets out the port corresponding to the computer connected to that port. The effect of this is it localizes traffic. This makes it possible to have maximum traffic on each port - less collisions. But even network switches are rare now for home use, because the router is more practical. Third, the router, is like a switch that pays attention to the IP (network) address of a packet instead of the MAC (physical) address. This allows you to create networks in your home. Why would you care? Let me explain. If you are given an IP address from your internet provider, that address is only intended for one computer. You could not use a hub or a switch to share that address with 2 or more computers. But a router acts like the one computer that will be using that IP address, while giving the computers in your home separate addresses on a different network. Your provider might have given you 64.102.5.211 as an address, but your computers on the home side of your router have addresses in the 192.168.1.1xx range (just as an example). Only a router can do this magic, and is why they are the most common network device sold for home users today. Home routers also allow for other neat tricks like allowing or blocking certain types of internet traffic. I hope I made that simple enough.