Thanksgiving is a national holiday celebrated on various dates in the United States, Canada, Grenada, Saint Lucia, and Liberia. It began as a day of giving thanks for the blessings of the harvest and of the preceding year. Similarly named festival holidays occur in Germany and Japan. Thanksgiving is celebrated on the second Monday of October in Canada and on the fourth Thursday of November in the United States and around the same part of the year in other places. Although Thanksgiving has historical roots in religious and cultural traditions, it has long been celebrated as a secular holiday as well.
Prayers of thanks and special thanksgiving ceremonies are common among most religions after harvests and at other times of the year. The Thanksgiving holiday’s history in North America is rooted in English traditions dating from the Protestant Reformation. It also has aspects of a harvest festival, even though the harvest in New England occurs well before the late-November date on which the modern Thanksgiving holiday is celebrated.
[The above information is from Wikipedia.]