What is Mothering Sunday?
Mothering Sunday in the UK is the equivalent of Mother's day in other countries

What happens on Mothering Sunday in the UK?
Mothering Sunday is a time when children pay respect to their Mothers. Children often give their Mothers a gift and a card. Some children also give them a little bunch of spring flowers to give to their Mothers as a thank you for all their care and love throughout the year.

When is Mothering Sunday (Mother's Day)?
Mothering Sunday (Mother's Day)  is not a fixed day because it is always the middle Sunday in Lent (which lasts from Ash Wednesday to the day before Easter Sunday). This means that Mother's Day in the UK will fall on different dates each year and sometimes even fall in different months.
This year it falls on 18th  March.

The History behind Mothering Sunday
Contrary to popular belief, Mother's Day was not conceived and fine-tuned by shopping centres, The earliest tributes to mothers date back to the annual spring festival the Greeks dedicated to Rhea, the mother of many deities, and to the offerings ancient Romans made to their Great Mother of Gods, Cybele. Christians celebrated this festival on the fourth Sunday in Lent in honor of Mary, mother of Christ. In England this holiday was expanded to include all mothers and was called Mothering Sunday.
This date  has been celebrated in the UK  since at least the 16th century.
Mothering Sunday is also sometimes know as Simnel Sunday because of the tradition of baking Simnel cakes.

The Simnel cake is a fruit cake. A flat layer of marzipan (sugar almond paste) is placed on top of and decorated with 11 marzipan balls representing the 12 apostles minus Judas, who betrayed Christ.
It was not eaten on Mothering Sunday because of the rules of Lent, instead it was saved until Easter.
The word simnel probably derived from the latin word ‘simila’, meaning fine, wheaten flour from which the cakes were made.
A Simnel is still made in many parts of England today, although it is now more commonly made for and eaten on Easter Day
 

 In the United States, Mother's Day is celebrated on the second Sunday of May.