milk truck · noun1
milk truck · noun2
Figuratively from the vehicle. Popularized through the video game War Thunder, which features many unprotected or lightly armored truck-like vehicles to play, like the soviet GAZ-MM and Sd.Kfz. 6/2, both visually similar to old milk trucks, but also sensitive to damage, like trucks loaded with glass milk bottles. Coined as early as 2014 when the game added playable ground vehicles, including said trucks, possibly coined by the content creator PhlyDaily.
Etymology from Wiktionary, CC BY-SA 4.0.