The models that make up your army must be formed into 'units' before battle commences, ideally when writing your muster list. A unit usually consists of several models of the same type that have banded together and adopted a specific formation.

Additionally, single, powerful models such as a character, a chariot or a Dragon, a war machine and its crew, and so on, are also considered to be a 'unit'. Therefore, whenever the rules that follow refer to 'units', this also includes units of one model.