The Creatures
Zombies: "Zombie" tends to be a slang term and isn't used very frequently, most likely an unconscious refusal to acknowledge the existence of what was previously just a "movie monster." It is also claimed that the term is incorrect because the current "zombies" are not just random corpses capable of reanimating themselves. A person who dies from any other method aside from infection from the virus will not suddenly return as a member of the Undead. The virus must be injected into the bloodstream to take affect, though in all other aspects, those who are infected fit all characteristics of the zombie profile. They are walking corpses, which means they are incapable of moving at the full speed of a living human. They can move at a swift walking pace if their limbs are not damaged, are capable of climbing, and may be seen alone or traveling in hordes. Actual communication doesn't seem to play into effect within a horde, but they will react to one another's energy signatures (ie, if one stiffens in response to a noise, the rest will stiffen even if they hadn't heard the noise). They have an insatiable hunger and infect others via their saliva passed through bite wounds, or by mixing their blood with that of a living organism. They can only be killed if their heads are severed from their bodies, or at least damaged enough that messages are no longer being relayed through the nervous system. More common names for zombies are Diseased, Infected, or Undead.
To change into a zombie is called "being turned." Once infected, the virus spreads through the body at alarming speeds. The idea of just cutting off a limb to prevent a turn has been proven ineffective. A human will become a full member of the Infected within an hour of exposure to the virus with varying symptoms taking hold during the process of dying. One of the symptoms is the loss of coloration in the eyes, turning both the iris and pupil a light blue prior to death, after which the eyes turn a milky white.
Hellhounds: The only people who knowingly use this term are the members of the Seven who adopted it from Josiah as the name for infected dogs. Animals cannot be turned in the same way that humans can, but some do succumb to many of the same behavioral traits as the Diseased. Hellhounds are incredibly violent and constantly hungry, particularly for live prey, but they are not dead, meaning they can be killed via any conventional means. The virus instead acts as a constant adrenaline boost, making them faster and stronger than an average canine would be in a relaxed state. Stuck in a stage of pre-death, the eyes of infected dogs are always pale blue and sensitive to bright light. They will come out during the day if there is prey to be hunted, but otherwise prefer to travel at night.