the number one thousand, the round figure used to count people, soldiers, animals, time, and value
This is the everyday counting word for a thousand. It carries most of the great tallies in the Bible: the marching numbers of Israel in the wilderness, the size of armies, the weight of silver and gold, the head count of livestock, the years of a long span. In the lists of Numbers and the war reports of Samuel, Kings, and Chronicles it is simply the largest ordinary unit a Hebrew writer reaches for before "ten thousand."
Because a thousand was already a very large number to an ancient reader, the same word often stops being an exact count and becomes a way of saying "a vast amount" or "as good as countless." Promises of a thousand generations, a wish for a thousand thousands of descendants, and the picture of one soldier putting a thousand to flight all lean on the size of the number rather than on the precise figure. The two uses sit on a single scale: a literal tally at one end, an open-ended "more than you can count" at the other.
The count and the round flourish are not always easy to tell apart, and a reader should not assume every "thousand" in a census is meant to be added up to the last digit. The point is usually the scale, not the arithmetic.