CharacterSpecies

In the Combat System, a character (or object's) SPECIES determines a few things about it.

Transformer
Most characters are of this species (obviously). Transformers can be repaired or patched by people with the REPAIR ability. (!repair)

Junkion
Note that Junkions are a separate species from Transformers! This means when you type !profile you should see something like this: =========================

Junkions are also repaired or patched by people with the REPAIR ability. However, unlike Transformers they can be patched an unlimited number of times during battle. They also are resistant to the system shock mechanic that automatically knocks targets unconscious when they receive more than <50% Endurance> damage from a single shot.

Junkions also have the cool junkdive ability when they are on Junkion.

Human
Hopefuly you are familiar with the term human! Human characters can be patched and repaired by those with the HEAL ability.

Alt-Human
There are not many of these left. Alt-Humans are former Militants and Benefactors -- human characters from an alternate universe that arrived during one of TF2005's first plots. Codewise they are no longer any different from humans.

Vehicle
Vehicles are things like Exo-Suits, Shuttles, Tanks, etc. They can be patched (yes) and repaired by those with the CONSTRUCTION ability. (!rebuild command)

Weapon
Weapon Objects are MUSH objects that interact with the combat system. Typically they sit in your inventory and give you access to extra attacks. Sometimes they sit out in a room so that multiple people can use them. If you have the CONSTRUCTION ability you can repair weapons. If you have the REFUEL or RELOAD ability you can use it on them as well.

Booster
Booster Packs are special objects that interact with the combat system, but are not themselves weapons. Instead they give players temporary bonuses during combat. They can not be patched or repaired.

Base
Bases are similar to weapons except they are usually meant to just sit in one location and not move around. Codewise they are the same as Weapons, able to be repaired by those with the CONSTRUCTION ability.