It refers to the act of writing a word using the correct sequence of letters.
Here are some ways "pagbabaybay" is used in Filipino:
* "Ano ang pagbabaybay ng salitang 'mahal'?" (What is the spelling of the word "mahal"?)
* "Magaling ka sa pagbabaybay." (You're good at spelling.)
* "Nahirapan ako sa pagbabaybay ng ilang salita." (I had difficulty spelling some words.)
So, whenever you see "pagbabaybay" in a Filipino context, you can understand it as referring to spelling.