Yummy mummy is a slang term used to describe an attractive mother.
The term developed in the late 20th century, and was often applied to celebrity mothers such as Elizabeth Hurley[1] or Victoria Beckham,[2] who appeared to quickly regain their pre-pregnancy figures after giving birth, and would continue to lead carefree and affluent lifestyles.
Episode 13 of series six of The Nanny (airing in 1999) was called "The Yummy Mummy".
A stereotypical yummy mummy was described by Nirpal Dhaliwal in The Times as having an existence "bankrolled by a husband working himself to death in the City, [dressing] in designer outfits... carries the latest must-have bag [and] whose hair and nails are perfectly groomed".
[1] Yummy mummy has a similar slang connotation to MILF, but suggesting a younger subject.