This cookery name is derived from the process to soak ingredients in soup stock, but this process is often skipped, and simply boiled foods with soy sauce on it is also called ohitashi.
出汁に浸す過程より派生した調理名であるが、この工程は省かれることも多く、単に茹でた食材に醤油をかけたものもおひたしと呼ばれる。