# physical significance of the 'time of relaxation ' and 'time of observation'

Deborah number (used frequently in rheology) is defined as the ratio of the time of observation to the time of relaxation. In his article The Deborah Number, M. Reiner the man who coined the term has mentioned that if the time of observation is high that is the time of relaxation is low, in other words if the Deborah number is less than 1 then it describes a flow.

How to interpret time of relaxation and time of observation? I tried Wikipedia but there isn't a very clear description of those 2 temporal entities.