When you translate it out it bits it’s the number of bits that are active in the net mask

0000 0000 0000 0000 0000 0000 0000 is a /0

0000 0000 1111 1111 1111 1111 1111 1111 is a /24

0000 0011 1111 1111 1111 1111 1111 1111 is a /26

And since it’s used for marching, it follows how many there are.