One of the things I worked on back when I worked on search stuff is now public, at least to the extent that it was mentioned in a presentation:
"GM" alone probably means "General Motors." But "GM foods" refers to genetically-modifed chow. "b&b ab" means "Bed and Breakfast in Alberta," but "ramstein ab" is an airbase.
(As always, I probably can't say anything more about how it works except to point out it's more than just abbreviations and more than just changing the highlighting in the results. But you can try the queries! Put a + before a term to tell Google "I mean only and exactly what I typed".)