That's the ability to instantly recognize the number of objects in a small set or arrangement without counting.
It's being able to instantly know the number of dots on a die...
or a domino...
Or for me, the number of cookies on a plate...mmm....6.
It's a developmental prerequisite to counting, and many kindergartners come to school without this skill. So it's essential for us to teach it!
If you're interested in the research behind this concept, here's an excellent article by Douglas H. Clements:
Teaching it is easy! The easiest way is just to flash dot cards and have the kids quickly call out the number. Here's something I put together...a quick powerpoint with dot arrangements. I flash each slide for just a few seconds. Most of the time, I just have the kids call out the number, but sometimes, I have them write the number on dry-erase boards or create the same pattern on their tables with counters.
There are also numerous games you can play with dot cards. The absolute best resource I have found is:
BRAVO to the Winnipeg School Division--I have used the activities in this book for years now. It is filled with SO MANY dot card actvities--and even has the dot cards in it. (And five and tens frame activities, as well.) Did I mention that it was free? So go grab it--NOW! (Click on the image.)
Interestingly enough, the word is pronounced soobitize--with a long u. One would think it was a short u, as in substitute teacher or submarine sandwich. But noooo... it's a long u like tuba-tize.