Some spells and war machines are so powerful that they don't just target a single model or unit, but have an 'area effect' which might encompass (and often utterly devastate) several different units. To better represent these, Warhammer uses a series of three different templates:
A small round template (3" in diameter)
A large round template (5" in diameter)
A flame template (a teardrop-shaped template roughly 8" long)
The templates are used as a way of determining whether or not models have been hit by an attack that has an area of effect or blast radius. When an attack uses a template, it will explain how the template is positioned, including any kind of scatter that might occur (scatter is discussed more completely next in this section). To work out which models are hit, you normally need to hold the template over an enemy unit or a particular point on the battlefield (as close to the battlefield or unit as possible), and then look underneath to see which models' bases lie partially or completely underneath the template.
Normally, any model that is fully or even partially underneath the template is hit automatically with the effect described in the special rules for the attack. Remember that a model’s base is counted as being part of the model itself, so as long as any part of the base is under the template everything is hit.