nodding acquaintance

noun

1. a slight, incomplete, or superficial knowledge (of something or someone): He had only a nodding acquaintance with Italian and didn’t trust it to get him through the tour. Although we were neighbors for several years, we had only a nodding acquaintance.
2. a person with whom one is only slightly acquainted: I don’t really know what he’s like—he’s only a nodding acquaintance.

Superficial knowledge of someone or something, as in I have a nodding acquaintance with the company president, or She has a nodding acquaintance with that software program. This expression alludes to knowing someone just well enough to nod or bow upon meeting him or her. “Early 1800s]