National Mac Day is celebrated annually on April 12, honoring the significance of the prefix "Mac," which means "son" in Gaelic and is commonly associated with surnames in Scotland, Ireland, and other regions with Irish and Scottish heritage. The day recognizes the historical context of these names, which often signify family lineage and ancestry. Notable Mac surnames include MacGregor, MacLeod, and MacAllan, reflecting their Norse and Gaelic origins. While the use of the "Mac" prefix declined in Ireland by the 1800s, it remains prevalent in Scotland, particularly among those with ties to their Gaelic roots. Celebrations may include gatherings among individuals with Mac surnames, as well as cultural activities that honor their heritage.