Fullness refers to the amount of reflected sound intensity relative to the intensity of the direct sound; the more reflected sound, the more `full' the hall will be. For slow, romantic music performed by very large groups, fullness is required, whereas chamber music or music from the classical or baroque periods does not require great fullness. In general, greater fullness implies a longer reverberation time.

Paul Horn: Inside the Great Pyramid
Carlos Nakai: Canyon Trilogy
Organ at Notre Dame de Paris
Orchestras: Classical, 19th Century, Organ, Voice