(Credit: Francis Flinch)
This is a small magnifying glass used for close-in work, like examining gems, watch-making, or surgery. They’re sometimes handheld and sometimes affixed to glasses.
Why I Looked It Up
On an episode of Chuck, the titular character discussed a loupe and used one to examine a gem.
I went to an eye doctor appointment, and the doctor looked into my eye with an illuminated magnifying glass. I asked him what it was, hoping he would say “loupe,” but – alas – he said it was a “convexing lens.” Sort of the same thing, though.