Croquis, although sounds like a pastry, it simply means 'sketch' in French. It is pronounced as \krō-ˈkē\ which is a noun of croquer, meaning to sketch. (From Merriam-Webster)
In fashion, it refers to a quick sketch of 'mannequin' modelling clothes that are being designed, and are usually not of realistic human proportions.
Here's a useful link for croquis (as shared by ladyjanewriter of Threadbanger Forum), http://www.designersnexus.com/tag/croqui/