Wearing a mask over your mouth, but not your nose.
Dave: Did you see that guy breathing all over the shelves?
Sarah: Yeah, he was flying at half mask.
When someone hangs their mask off one of their ears
The grocery worker was scolded by his manager fot being half masked while filling the shelves.
Someone who you see in a public setting with a mask on but barely on their face or just covering their lips
Dude 1: I was at Costco and this guy had a mask on but it was just slightly covering his mouth.
Dude 2: oh he out here Half Masking