"GDA" refers to Guideline Daily Amounts, a nutrition label that appeared on foods in the United Kingdom beginning in 1998 and continuing into 2014. According to Wikipedia, as of 2014, GDAs began to be replaced by "reference intakes."
According to the U.K. Food and Drink Federation, GDAs provide information regarding the optimal intake of calories, proteins, carbohydrates, sugars, fats, saturated fat, fiber and salt. Nutrition labels on food list the percentage of the GDA for different nutrients that the food provides. Separate GDAs exist for men, women and children. In the United Kingdom, any GDAs printed on the front of food packages are those aimed at women.