Mothering Sunday (as opposed to Mother's Day) is a church festival which falls on the fourth Sunday in Lent, and so the date varies from year to year. And the mother in Mothering Sunday is not your female parent, but your Mother Church - that is, the Church where you were baptised. On Mothering Sunday you were supposed to attend the services at you Mother Church. Of course, if you'd moved away, this would involve going back home and you would doubtless take the opportunity to visit your parents, and take a bunch of flowers for your mother...