TERC Math – please explain

Last month I attended a preview day for a charlotte mason school here in our city.  The director said that they are using TERC math.  She did not spend anytime explaining it and I was curious so I have been “googlng it” and I am having a hard time understanding the concept.  Can someone break it down for me in “non-math terms” and are there homeschool cirriculums that use this approach? 

Thanks, Amy