All buses consist of two parts -- an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go.

The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data.

Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old ISA bus is being replaced by faster buses such as PCI.

Nearly all PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor.  Several different types of buses are used on Apple Macintosh computers. Older Macs use a bus called NuBus, but newer ones use PCI.

See also "Understanding PC Buses" in the Did You Know...? section of Webopedia

(2) In networking, a bus is a central cable that connects all devices on a local-area network (LAN). It is also called the backbone.

PC system bus reference guide 
A complete look at the PC's system I/O buses. Includes coverage of the various functions and features of the bus, a look at ISA, VLB and PCI buses, plus older technologies, and the new AGP port.

PC motherboard and system device reference
Comprehensive motherboard reference, covering all the major motherboard components. Looks at the physical motherboard, chipset, system buses, system cache, system resources, and the system BIOS.

Troubleshooting the Motherboard and System Devices
Focuses on problems related to the motherboard and system devices, including the components of the motherboard, along with system devices such as the cache and I/O buses, the BIOS and CMOS memory, system resources, and features such as Plug and Play. This page is from "The PC Guide."

Yahoo!'s buses page
Yahoo!'s directory of buses.

Yahoo!'s universal serial bus page
Yahoo!'s directory of universal serial bus.

Hardware Central
Detailed test reports on the latest desktop and laptop computers. Plus news on trend-setting products just coming into the pipeline.

Microprocessor Comparison Chart
A cut-to-the-chase guide that compares and contrasts popular processing chips.

Webopedia's "Did You Know... Understanding PC Buses"
Think of a bus as the electronic highway on which data travels within a computer, from one component to another. Basically, it's the conduit used by your entire system to communicate with your CPU.