The maximum number of bits per instruction that a CPU can process during 1 machine cycle is called word size.
Several word sizes form data bus size, instruction size or address size.
Word size is the smallest piece of data the processor can fetch from memory. The word size starts with 4-bit, 6-bit, 8 bit, 12 bit, 16 bit, 18 bit, 20 bit, 24 bit, 32 bit, 36 bit, 64 bit, and up.