A mother is called ‘tiger’ when she is very tough and a bit scary. Most Westerners were not familiar with this term, until a book was published.
The term ‘tiger mother’ (or tiger mum) comes from the book ‘Battle Hymn of the Tiger Mother by Amy Chua. It can be used as a verb too – ‘to tiger mother’.
Chinese mums are usually called ‘tiger mothers’ and some strict fathers are called tiger dads!