Short for "Zoom Direct Message" . To chat another person in the zoom while on a zoom meeting. If two people start laughing at the same time, they are undoubtable ZDMing each other about you.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.