Chapter one of the forms book, at http://www.symfony-project.org/book/forms/1_1/en/01-Form-Creation, uses the word imbricate twice. The first says "we will see later how useful and easy it is to imbricate forms", and the second says "makes it easier to manage imbricated forms".
Apart from being obscure, imbricate means overlapping, like fish scales or roof shingles. I suppose there might be some elegant uses of overlapping forms, but I can't think of any. Since chapter 5 of the forms book isn't available yet, I can't tell what is really intended, but imbricate is clearly the wrong term here.
