The Collaborative International Dictionary of English v.0.48:

Mother's Day \Moth"er's Day\
   A day appointed for the honor and uplift of motherhood by the
   loving remembrance of each person of his mother through the
   performance of some act of kindness, visit, tribute, or
   letter. The founder of the day is Anna Jarvis, of
   Philadelphia, who designated the second Sunday in May, or for
   schools the second Friday, as the time, and a white carnation
   as the badge.
   [Webster 1913 Suppl.]