'man ps': What is the difference between 'CODE' and 'HEADER'?

[Tom H]

> 'man ps' in the section "STANDARD FORMAT SPECIFIERS" lists a table
> headlined "CODE HEADER DESCRIPTION" to control the output format of the
> ps command. When do I have to use 'CODE', and when do I have to use
> 'HEADER'?
> What is the difference between the two?

"Code" = what you type in after the "-o"
"Header" = what is printed out at the top of the ps output columns
"Description" = man page explanation of the "Code"