Data bus width is how much data the CPU can communicate with the rest of the motherboard at a time. The CPU manufacturer determines this when they design the CPU.

The first IBM-compatible CPU could only communicate 8 bits at a time! This number jumped to 16, then to 32, and then to 64. We have come a long way with current CPU technology. CPU manufactureres are constantly pushing the limits to increase this number.

The important thing to remember is, the larger this number the more data your CPU can communicate at a time. In other words, the higher the number, the faster your PC.