How do I make a table cell a header?

Or is there nothing in Word for specifying a cell as a header? I sure
thought I had done that but it has been a long time. Perhaps I am just too
accustomed to HTML, in which there are separate tags for header cells.

I looked in the Word documentation and could not find anything, except
something describing how to "Repeat a table heading on subsequent pages",
which sure implies that there is something such as "a table heading" in Word
too. If that is true, then it is impossible to find in the Word
documentation how to make them. If that is not true, then the haeding
"Repeat a table heading...." is sure misleading.