Ovomancy was a type of divination that involved cracking open eggs and observing which way the yolks fell. Robert Hilliard, a Ravenclaw Prefect in the 1990s, informed first years who had just been Sorted into Ravenclaw that this was not considered an unusual pastime within the House. In fact, according to him, not only would other Ravenclaws have no trouble with someone "spend[ing] [their] days and nights" practising ovomancy in a corner of the common room, but one would "probably find a few people to help."
Ovomancy comes from the Latin word 'ovo', meaning 'egg'.
- Pottermore (Mentioned only)