forty: the cardinal number 40
This is simply the number forty. Most of the time it counts real things exactly: forty people in a census, forty cubits in a building, forty years of a king's reign, a man forty years old. In those places it carries no special weight, the way the English word forty carries none.
The one nuance worth knowing is that forty is also the Bible's favorite round number for a long, full stretch of time, especially when that stretch is a season of testing, waiting, or transition. The flood lasted forty days, Israel wandered forty years, Moses stayed on the mountain forty days and forty nights, and after several of the judges the land had rest forty years. In settings like these forty often signals a complete period rather than a figure counted to the unit, though the writers themselves do not separate the two uses, and many cases sit comfortably as both.
Readers should resist forcing every forty into a hidden code. The number's symbolic pull is real and the lexicons note it, but it grows out of ordinary usage. A reign or an age or a wall measurement of forty is usually just that.