Data word
A data word is a fixed-sized group of binary digits or bits that represent a piece of data. It is a standard unit utilized with computer systems whose size is dictated by the type of processor in the device. A data word determines how much input the internal data registers of a CPU (central processing unit) can work with at one time.
Essentially, a data word specifies the largest basic unit a processor can use to manipulate data. If the data is larger, it must be split and processed in multiple steps. A good way to think of it is as a "box" with particular dimensions (meaning it's always the same length, width, or size).
Efficiency
A computer generally processes information faster as the size of the data word increases. That said, the speed boost is influenced by the size or packaging of the data being processed. For example, when comparing a computer with 32-bit registers to one with 16 bits (same clock speed), adding a 16-bit number doesn't result in faster processing, but a 24-bit number does. Essentially, the 16-bit computer has extra steps (processing 16 bits first and then the remaining 8), while all 24 bits of the number can be accommodated in the 32-bit register.
Examples
A 64-bit computer architecture has a data word that is 64 bits long. At each step, it can process 64 bits or less without splitting data.
Other sizes, such as 8, 16, and 32 bits, are used in embedded processors for appliances like Smart TVs. These tend to have fewer instruction set commands and process smaller blocks of data.