What is biblical numerology?

Biblical numerology is a complex subject which can't be fully discussed here, but basically it concerns the recurring numbers in Scripture. It would appear that numbers in Scripture were constantly used to denote certain things. For example, 40 was often the number used to denote probation. The number 7 is thought to stand for God's perfection while 6 is the number of man, 4 the world, 5 grace, 8 resurrection, 9 finality etc. There are reasons for these. Biblical numerology goes further when Gematria is considered. All Hebrew and Greek letters have numerical value and when these are applied to words and verses in the Bible we see some amazing things. The subject is too vast for here. There are many books on the subject and if you are interested I'd suggest you obtain one.