What in reverberation? How can it be reduced?

Hint: As reverberation represents the effect of reflected sound from the surface of an enclosure. As multiple reflections that opposes the source to produce sound. So we can say absorbers of sound can be used to reduce that effect.

Complete step-by-step answer:
When a sound source is producing sound in a plain closed room then the sound produced gets reflected and this reflected sound takes multiple reflections which disturbs the sound produced by the source and stops / opposes it to produce the sound. This phenomenon of multiple reflections of the sound is known as reverberation. This reverberation can be reduced if we use things that can absorb the reflected sound.

Example: Thermocol, wood etc are some of the things or substances that are used in ceiling to absorb this reflection effect and reduce reverberation.

For example:
In Cinema theater there are multiple reflections of the Sound produced by the Speakers but we will not feed the effect of reflection of sound.
This is because the ceiling of the theater hall u Covered with the thermocol Sheets which absorbs the sound reflection and hence we can hear clear sound from the Speakers without any disturbance.

Note: Echo and reverberation are different. The reverberation actually produced after the sound from the source stops and makes up to feel the sound repeatedly. Whereas echo can be produced when a sound is heard twice with the same pulse.