Digit placeholder

[lezawang]

Hi
I am trying to understand custom excel number format. So I am reading the article below. It says # is digit placeholder....
What does that mean? what does placeholder means here? Thanks

https://support.office.com/en-us/article/Number-format-codes-5026bbd6-04bc-48cd-bf33-80f18b4eae68

 

[Kenneth Hobson]

Numerical digits would be number 0 to 9. # means that location can be any numerical digit. A 0 has a more special meaning. e.g. 5 with "#.00" would be 5.00.