Mean – because there are many and many millions absolute values which are absolutely useless, but mean value is the only and it have a practical meaning.
Dear Daouda!
For example, if
T1, T2, T3,….Tn are absolute values of different call durations.
Then Mean Call Duration = (T1+T2+T3+….+Tn)/n.
Are there enough for your understanding this problem? Or additional information is needed for you?