Subitizing is the visual perception of number quantities. It builds early concepts for place value, quantity, and addition/subtraction strategies. It is a foundational mathematics skill, and one that teachers incorporate into games for toddlers, preschool, Pre-K, and even older students. And it is a word you can impress people with (it is pronounced like scuba-tizing, without the “c” in scuba).
Try it out for yourself: In this image, there is a long row of dots. Can you tell how many there are at a quick glance? Most people cannot without counting them. In the image below, where the dots are grouped like they are on dice, most people can quickly recognize the quantity. Both images have 10 dots.