Like pfff, bah, oh là là, hopla and miam, tac is not itself a word. A Metro employee could say tac - tac - tac - tac while flipping through your tickets. In this example, tac is used to verify that all the tickets are there. Eeeet tac (peanut butter hits the table). Planning on reading The Local's French word of the day?

Source: The Local January 10, 2020 09:00 UTC