fuller explanation can be found on Wikipedia.
Why is it important to us here in Guyana? Because as it moves over Guyana it is largely responsible for our rainy seasons. Which brings me to the nice picture I took off the BBC weather web site on the 22nd. The ITCZ was hanging around our latitude for longer than usual right up to mid-August. It is now well north of us and our weather much drier - see the green dots on the picture along the top marking the band of cloud where the ITCZ is located now.
In a few months it is expected to drift south again bringing our next rainy season in November.
It is of little interest to US media where most of our television originates which may explain why few people here seem to know about it. However there is a good explanation of its effect on the Hydromet web site.