Of or involving the cells of an organization or movement: The assessment of opposition to any totalitarian regime ... is notoriously difficult, for any effective movement must be secretive and cellular (Anthony Sampson). 4. Of or relating to a cellular telephone.
In the past, a human generation has been considered to be 20-25 years. Older genealogical documents will use these numbers. However, genealogical studies have revealed that this is too simplistic and can result in large inaccuracies during statistical calculation.
To summarize: A generation in the bible is primarily the age of a man when his first male child is born; but secondarily, the age of a man at his death. The bible then rounds the exact span of years in a generation to be 40 and 100 years as the primary usage, but on occasion, 70 years. And 70 is the average of 40 and 100, which allow the three timeframes to work in numeric harmony to produce the numeric symmetry found throughout the bible.