a frill
yes
It uses its frill of bone around its neck and shoulders and sharp horns
The dinosaur with three horns is called the "Triceratops". It is a large plant eater with a frill protecting it's neck. The Triceratops uses the horns for spearing plants, and as weapons to protect itself from predators.
No, Triceratops wasn't armored. Its large neck frill provided a small amount of protection for its neck, but it doesn't qualify as armor.
It is called the Nape
A triceratops main defence was it's three horns hence the name but it also had a hard bone crest that protected the neck it was believed to live in packs or herds these reptiles weight about four tons it was a walking tank
Axis
They are called vertebrae. Specifically in the neck they are called cervical vertebrae, the lower back are called lumbar vertebrae and the mid back around the ribcage are called thoracic vertebrae.
The medical term for a neck joint is called a pivot joint. This is when one bone rotates around another bone in a circular motion.
No one knows if any dinosaurs have a frill, but you are probably thinking of Dilophosaurus.
The three horns (made of bone, instead of usual ivory or keratin) on its head, the frill, and in some ways, the pelvic bone. It had a ball-and-socket joint instead of a pivot joint connecting its head to the neck vertebrae. This was the only organism in the fossil record to have this adaptation.
I'm pretty sure it is called the Atlas bone, right where the skull meets the neck.