A data bus is a communication system that transfers data between components inside a computer or between computers. It consists of a set of physical connections, such as wires or traces on a circuit board, that carry data signals. Data buses are essential for enabling different parts of a computer, like the CPU, memory, and input/output devices, to communicate effectively. Data buses can vary in size and speed, with wider buses capable of transferring more data at once. Common types include the address bus, which specifies memory locations, and the data bus, which carries the actual data. The efficiency of a data bus can significantly impact a computer's overall performance.