Depending on the region you live in, it's also frequently called a "dolly"

Isn’t a dolly a flat 4 wheeled platform thingy? A hand truck is the two wheeled thing that tilts back.

Ha! Where I'm from a "dolly" was the two-wheeled thing. The four-wheeler thing wasn't common before big-boxes took over the hardware business, but I think my dad would have called it a "cart", maybe a "hand-cart".

Grew up with two wheeled: dolly and four wheeled: piano dolly. Was an adult when I heard hand-truck. I prefer dolly. Nicer mouth feel.