约数 has two distinct senses that are unrelated in English. In everyday life it means 'approximate number' — a round figure like 'about 100 people' (约一百人). In mathematics it's the term for 'divisor' — a number that divides another evenly, like 3 is a divisor of 9. When reading math contexts, be aware that 最大公约数 means 'greatest common divisor' (GCD). The two senses don't overlap, so context is key.