Define 'flammability'.

Flammability is defined as the ability of a substance to ignite and sustain combustion. This definition captures both the ignition of the material and its continued burning once it has been ignited. Flammability is an essential property in the context of hazardous materials, as it directly relates to the potential risk a substance poses in terms of fire hazards.

While the other options provide related concepts, they do not fully encompass what flammability entails. For example, one option describes the ignition point, which refers specifically to the temperature needed to start combustion, but does not address whether the substance can continue to burn. Another option relates to the speed of combustion, which is more about the rate at which the reaction occurs rather than the essential ability to ignite and sustain combustion. Lastly, one choice discusses the energy released during combustion, which is a characteristic of the combustion process, yet it does not clearly define flammability itself. Therefore, understanding flammability as the capacity to ignite and maintain combustion is crucial for recognizing and managing risks associated with hazardous materials.