Character models are a special type of unit that can either operate on their own, or that can join another unit belonging to their army. They usually have superior characteristic values compared to ordinary members of their race, often have a number of special rules (sometimes unique) and invariably have more options in terms of equipment, including access to highly prized magic items.
All character models will have the word 'Character' in brackets after their troop type. This indicates that a model is a character and, as such, follows the rules given here.