With reverb, we understand the reflection of sound waves in a room. The duration of a sound will typically be longer and the overall sound a bit more diffuse when reverberation is added. We will look more in detail on reverberation in later lectures, but for now, let's get started in listening to and identifying it. The excersises here are concerned with reverb time and reverb mix. Reverb time can be defined as the time it takes for the reverberation to die out, i.e. become inaudible. The time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer. In order to provide a reproducible parameter, a standard reverberation time has been defined as the time for the sound to die away to a level 60 decibels below its original level. For more info see e.g.: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/revtim.html.
The reverb mix parameter defines the balance between dry and reverberated sound.