In a modern system of classification, all animals can be divided into two groups – vertebrates and invertebrates. Vertebrates are animals that have a skeleton inside their bodies. Biologists call this an internal skeleton
An internal skeleton includes a backbone which is made up of bones called vertebrae
Vertebra is one bone in a backbone; vertebrae is more than one bone from a backbone.
Frogs have a short backbone (spine)., with a large hip bone to support their powerful leg muscles, therefore, frogs are vertebrate. Examples of vertebrates include humans, dogs, cats, birds, snakes, crocodiles, turtles, frogs, lizards and fish.
The presence of a skeleton, or an endoskeleton, is not restricted to vertebrates. for example, spiders and other arachnids have cartilagenous endosternites and internal apodemes in addition to the “exoskeleton” that is so well-known. Amphioxus is a chordate, as are all vertebrates, but it is not a vertebrate because although it has a firm notochord as an internal skeletal element, it does not have segmental vertebrae along the anterior-posterior axis of the body. The vertebrates, or members of the clade Vertebrata, are simply the animals that have these vertebrae. This includes fish, amphibians (including frogs), reptiles, birds and mammals. In sharks the vertebrae are not bony, but cartilagenous, but they are still present and sharks are also vertebrates. By far the most diverse group of vertebrates is the Osteichthyes (bony fish), but this is not a clade as all amphibians, reptiles, birds and mammals are descended from this group, and all have vertebrae built of true bone.