A bus interface is a communication system that transfers data between components inside a computer or between computers. It allows different parts, like the CPU, memory, and peripherals, to connect and share information efficiently. Bus interfaces can be parallel, where multiple bits are sent simultaneously, or serial, where data is sent one bit at a time. Common types of bus interfaces include USB (Universal Serial Bus), which connects devices like keyboards and mice, and PCI (Peripheral Component Interconnect), used for adding hardware like graphics cards. These interfaces help standardize connections, making it easier to expand and upgrade computer systems.