Just for completeness, definitions of both terms from WordNet:
heading
n 1: a line of text serving to indicate what the passage below
it is about; "the heading seemed to have little to do with
the text" [syn: {heading}, {header}, {head}]
headline
n 1: the heading or caption of a newspaper article [syn:
{headline}, {newspaper headline}]-- : Eric S Fraga via Emacs 28.0.50, Org release_9.4.6-598-g604bfd : Latest paper written in org: https://arxiv.org/abs/2106.05096
