What is 'Día de los Reyes'?
It means three kings day.
On January 6, most of the Hispanic world celebrates El Dia De Reyes, the Epiphany, remembering the day when the Three Wise Men following the star to Bethlehem, arrived bearing their treasured gifts of gold, frankincense and myrrh for the Baby Jesus.
The meaning of Epiphany...
Epiphany is a complex feast. Originating in the Eastern Church and formed by the mentality of a people whose thought processes differ sharply from our own.
- an appearance or manifestation especially of a divine being.
In Mexico and many other Latin American countries, Santa Claus isn't like he is in the United States. It is the three wise men who are the bearers of gifts, who leave presents in the shoes of children. The holiday is also known by the name of the Epiphany which dates back to the 4th century. A grand feast would be held on this day to honor the occasion of Jesus' baptism and to pay homage to the three wise men.
Many believe mysterious events preceded Jesus' birth with perhaps the most notable being the appearance of the Star of Bethlehem. This new star appeared in the evening sky just prior to the arrival of Jesus. Three wise men or Magi as they were then known, whose names were Gaspar, Melchior and Balthasar, traveled a far distance to pay homage to the Christ child. They brought with them fine gifts of gold, frankincense and myrrh.
Three Kings Day remains an important holiday for the people of Mexico. In addition to the gift-giving aspect of the day there is also a culinary treat that is specific to the holiday. Known as 'Rosca de Reyes' (King's Cake), this holiday dessert offers much in the way of symbolism. Shaped in the round to signify a king's crown, this sweet bread holds a special surprise. Baked inside is a small plastic figurine representing the baby Jesus. Whoever finds this token is obligated to host an upcoming party for the occasion of 'Dia de la Candelaria' (Candlemas Day) which occurs each year on February 2nd.
This info is from http://www.mexonline.com/history-lostresreyes.htm
And Google images