You have probably heard that a specific (computer) processor has such or so bits wide processor.

This number indicates how many bits a processor can handle at the same time.

This is called word length.

Hence the number of characters or bits in a word.

It is also an indication of how fast a machine is. Or better how fast a computer can deal with a program's instructions.

For example the Intel 4004 CPU invented in 1969 (published in 1971) has a speed of 60.000 operations per second.

A program is a collection of commands that in their turn are a collection of instructions to the microprocessor.
Each instruction can be translated to a certain length in bits. So the larger the number of bits a processor can deal with the more instructions a computer can handle and the faster it will appear.

Or to say it differently when you can put larger, and thus more complex, instructions to a computer's microprocessor the faster a computer can execute a command and so a program will appear to be faster.

However this is not allways the case. The processor needs time to process a command, a word. And the longer that command is the more time it takes to proces that command.(1)
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Also the more complex commands are stored in the processor, the longer it takes to find that specific command in its processor table, when the program feeds that command to the processor. It is like running off a list of addresses on a sheet and the address tells you where to go.

Engineers decided that it is not always necessary to have the full complex command list to one's disposal and created a more symplified command structure: RISC = Reduced Instruction Set for Computers. The advantage is obvious.
The wordlength is also shorter and thus this processor will run faster than the CISC based processors.

With various tricks