When I was going for my MA in special education, and received my certification, 13 years ago, I did my student teaching in a EMR classroom, educable mentally retarded. There are also severely retarded, profounly retarded, etc., based on IQ scores. It's a term commonly used in special education, a term not appropriate for use when not in terms of special education. However, the PP did use it in an appropriate manner.Call it whatever you want. It is offensive to many, many, many people.