1260 days, 42 months or 3.5 years.
It is the period that God allows the beast to operate.
Two female bears kill forty two children after they ridiculed the prophet of God. 2 Kings 2: 24.
Israel camped 42 times in the wilderness during the 40 year exodus, when the cloud moved.
The goat's hair and linen curtains covering the sanctuary have a length of 42 and 40 cubits.
Jesus was forty two generations from Abraham. (Matthew 1). He was also seventy seven generations from Adam. (Luke 3)