WHAP is an Elvin acronym, which means/stands for 'Wash Hands And Present'.
This acronym was mentioned in the first book during Alchemy, where Sophie read it as “WHIP”, and she therefore ruined the potion she was making and causing Keefe to call it the Great Cape Destruction (involving one Lady Galvin's capes which was one of her most prized possessions). It was later explained to Sophie by Elwin, who claimed that it was an honest mistake that could've happened to anyone.